diff --git a/api/database.py b/api/database.py
index e7bcf46..271b7cc 100644
--- a/api/database.py
+++ b/api/database.py
@@ -6,11 +6,27 @@ SQLite database schema for feature storage using SQLAlchemy.
 """
 
 import sys
-from datetime import datetime
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import Optional
 
-from sqlalchemy import Boolean, Column, DateTime, ForeignKey, Integer, String, Text, create_engine, text
+
+def _utc_now() -> datetime:
+    """Return current UTC time. Replacement for deprecated _utc_now()."""
+    return datetime.now(timezone.utc)
+
+from sqlalchemy import (
+    Boolean,
+    CheckConstraint,
+    Column,
+    DateTime,
+    ForeignKey,
+    Integer,
+    String,
+    Text,
+    create_engine,
+    text,
+)
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import Session, relationship, sessionmaker
 from sqlalchemy.types import JSON
@@ -65,6 +81,14 @@ class Schedule(Base):
 
     __tablename__ = "schedules"
 
+    # Database-level CHECK constraints for data integrity
+    __table_args__ = (
+        CheckConstraint('duration_minutes >= 1 AND duration_minutes <= 1440', name='ck_schedule_duration'),
+        CheckConstraint('days_of_week >= 0 AND days_of_week <= 127', name='ck_schedule_days'),
+        CheckConstraint('max_concurrency >= 1 AND max_concurrency <= 5', name='ck_schedule_concurrency'),
+        CheckConstraint('crash_count >= 0', name='ck_schedule_crash_count'),
+    )
+
     id = Column(Integer, primary_key=True, index=True)
     project_name = Column(String(50), nullable=False, index=True)
 
@@ -87,7 +111,7 @@ class Schedule(Base):
     crash_count = Column(Integer, nullable=False, default=0)  # Resets at window start
 
     # Metadata
-    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    created_at = Column(DateTime, nullable=False, default=_utc_now)
 
     # Relationships
     overrides = relationship(
@@ -131,7 +155,7 @@ class ScheduleOverride(Base):
     expires_at = Column(DateTime, nullable=False)  # When this window ends (UTC)
 
     # Metadata
-    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    created_at = Column(DateTime, nullable=False, default=_utc_now)
 
     # Relationships
     schedule = relationship("Schedule", back_populates="overrides")
diff --git a/progress.py b/progress.py
index dfb700b..a4dda26 100644
--- a/progress.py
+++ b/progress.py
@@ -10,7 +10,7 @@ import json
 import os
 import sqlite3
 import urllib.request
-from datetime import datetime
+from datetime import datetime, timezone
 from pathlib import Path
 
 WEBHOOK_URL = os.environ.get("PROGRESS_N8N_WEBHOOK_URL")
@@ -171,7 +171,7 @@ def send_progress_webhook(passing: int, total: int, project_dir: Path) -> None:
             "tests_completed_this_session": passing - previous,
             "completed_tests": completed_tests,
             "project": project_dir.name,
-            "timestamp": datetime.utcnow().isoformat() + "Z",
+            "timestamp": datetime.now(timezone.utc).isoformat().replace("+00:00", "Z"),
         }
 
         try:
diff --git a/server/routers/schedules.py b/server/routers/schedules.py
index 6138824..7c6c4ed 100644
--- a/server/routers/schedules.py
+++ b/server/routers/schedules.py
@@ -8,10 +8,16 @@ Provides CRUD operations for time-based schedule configuration.
 
 import re
 import sys
+from contextlib import contextmanager
 from datetime import datetime, timedelta, timezone
 from pathlib import Path
+from typing import Generator, Tuple
 
 from fastapi import APIRouter, HTTPException
+from sqlalchemy.orm import Session
+
+# Schedule limits to prevent resource exhaustion
+MAX_SCHEDULES_PER_PROJECT = 50
 
 from ..schemas import (
     NextRunResponse,
@@ -48,8 +54,15 @@ def validate_project_name(name: str) -> str:
     return name
 
 
-def _get_db_session(project_name: str):
-    """Get database session for a project."""
+@contextmanager
+def _get_db_session(project_name: str) -> Generator[Tuple[Session, Path], None, None]:
+    """Get database session for a project as a context manager.
+
+    Usage:
+        with _get_db_session(project_name) as (db, project_path):
+            # ... use db ...
+        # db is automatically closed
+    """
     from api.database import create_database
 
     project_name = validate_project_name(project_name)
@@ -68,7 +81,11 @@ def _get_db_session(project_name: str):
         )
 
     _, SessionLocal = create_database(project_path)
-    return SessionLocal(), project_path
+    db = SessionLocal()
+    try:
+        yield db, project_path
+    finally:
+        db.close()
 
 
 @router.get("", response_model=ScheduleListResponse)
@@ -76,9 +93,7 @@ async def list_schedules(project_name: str):
     """Get all schedules for a project."""
     from api.database import Schedule
 
-    db, _ = _get_db_session(project_name)
-
-    try:
+    with _get_db_session(project_name) as (db, _):
         schedules = db.query(Schedule).filter(
             Schedule.project_name == project_name
         ).order_by(Schedule.start_time).all()
@@ -100,8 +115,6 @@ async def list_schedules(project_name: str):
                 for s in schedules
             ]
         )
-    finally:
-        db.close()
 
 
 @router.post("", response_model=ScheduleResponse, status_code=201)
@@ -111,9 +124,18 @@ async def create_schedule(project_name: str, data: ScheduleCreate):
 
     from ..services.scheduler_service import get_scheduler
 
-    db, project_path = _get_db_session(project_name)
+    with _get_db_session(project_name) as (db, project_path):
+        # Check schedule limit to prevent resource exhaustion
+        existing_count = db.query(Schedule).filter(
+            Schedule.project_name == project_name
+        ).count()
+
+        if existing_count >= MAX_SCHEDULES_PER_PROJECT:
+            raise HTTPException(
+                status_code=400,
+                detail=f"Maximum schedules per project ({MAX_SCHEDULES_PER_PROJECT}) exceeded"
+            )
 
-    try:
         # Create schedule record
         schedule = Schedule(
             project_name=project_name,
@@ -178,9 +200,6 @@ async def create_schedule(project_name: str, data: ScheduleCreate):
             created_at=schedule.created_at,
         )
 
-    finally:
-        db.close()
-
 
 @router.get("/next", response_model=NextRunResponse)
 async def get_next_scheduled_run(project_name: str):
@@ -189,9 +208,7 @@ async def get_next_scheduled_run(project_name: str):
 
     from ..services.scheduler_service import get_scheduler
 
-    db, _ = _get_db_session(project_name)
-
-    try:
+    with _get_db_session(project_name) as (db, _):
         schedules = db.query(Schedule).filter(
             Schedule.project_name == project_name,
             Schedule.enabled == True,  # noqa: E712
@@ -245,18 +262,13 @@ async def get_next_scheduled_run(project_name: str):
             active_schedule_count=active_count,
         )
 
-    finally:
-        db.close()
-
 
 @router.get("/{schedule_id}", response_model=ScheduleResponse)
 async def get_schedule(project_name: str, schedule_id: int):
     """Get a single schedule by ID."""
     from api.database import Schedule
 
-    db, _ = _get_db_session(project_name)
-
-    try:
+    with _get_db_session(project_name) as (db, _):
         schedule = db.query(Schedule).filter(
             Schedule.id == schedule_id,
             Schedule.project_name == project_name,
@@ -278,9 +290,6 @@ async def get_schedule(project_name: str, schedule_id: int):
             created_at=schedule.created_at,
         )
 
-    finally:
-        db.close()
-
 
 @router.patch("/{schedule_id}", response_model=ScheduleResponse)
 async def update_schedule(
@@ -293,9 +302,7 @@ async def update_schedule(
 
     from ..services.scheduler_service import get_scheduler
 
-    db, project_path = _get_db_session(project_name)
-
-    try:
+    with _get_db_session(project_name) as (db, project_path):
         schedule = db.query(Schedule).filter(
             Schedule.id == schedule_id,
             Schedule.project_name == project_name,
@@ -337,9 +344,6 @@ async def update_schedule(
             created_at=schedule.created_at,
         )
 
-    finally:
-        db.close()
-
 
 @router.delete("/{schedule_id}", status_code=204)
 async def delete_schedule(project_name: str, schedule_id: int):
@@ -348,9 +352,7 @@ async def delete_schedule(project_name: str, schedule_id: int):
 
     from ..services.scheduler_service import get_scheduler
 
-    db, _ = _get_db_session(project_name)
-
-    try:
+    with _get_db_session(project_name) as (db, _):
         schedule = db.query(Schedule).filter(
             Schedule.id == schedule_id,
             Schedule.project_name == project_name,
@@ -367,9 +369,6 @@ async def delete_schedule(project_name: str, schedule_id: int):
         db.delete(schedule)
         db.commit()
 
-    finally:
-        db.close()
-
 
 def _calculate_window_end(schedule, now: datetime) -> datetime:
     """Calculate when the current window ends."""
diff --git a/server/services/assistant_database.py b/server/services/assistant_database.py
index 3c5ee44..176768e 100644
--- a/server/services/assistant_database.py
+++ b/server/services/assistant_database.py
@@ -7,7 +7,7 @@ Each project has its own assistant.db file in the project directory.
 """
 
 import logging
-from datetime import datetime
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import Optional
 
@@ -19,6 +19,11 @@ logger = logging.getLogger(__name__)
 Base = declarative_base()
 
 
+def _utc_now() -> datetime:
+    """Return current UTC time. Replacement for deprecated datetime.utcnow()."""
+    return datetime.now(timezone.utc)
+
+
 class Conversation(Base):
     """A conversation with the assistant for a project."""
     __tablename__ = "conversations"
@@ -26,8 +31,8 @@ class Conversation(Base):
     id = Column(Integer, primary_key=True, index=True)
     project_name = Column(String(100), nullable=False, index=True)
     title = Column(String(200), nullable=True)  # Optional title, derived from first message
-    created_at = Column(DateTime, default=datetime.utcnow)
-    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    created_at = Column(DateTime, default=_utc_now)
+    updated_at = Column(DateTime, default=_utc_now, onupdate=_utc_now)
 
     messages = relationship("ConversationMessage", back_populates="conversation", cascade="all, delete-orphan")
 
@@ -40,7 +45,7 @@ class ConversationMessage(Base):
     conversation_id = Column(Integer, ForeignKey("conversations.id"), nullable=False, index=True)
     role = Column(String(20), nullable=False)  # "user" | "assistant" | "system"
     content = Column(Text, nullable=False)
-    timestamp = Column(DateTime, default=datetime.utcnow)
+    timestamp = Column(DateTime, default=_utc_now)
 
     conversation = relationship("Conversation", back_populates="messages")
 
@@ -175,7 +180,7 @@ def add_message(project_dir: Path, conversation_id: int, role: str, content: str
         session.add(message)
 
         # Update conversation's updated_at timestamp
-        conversation.updated_at = datetime.utcnow()
+        conversation.updated_at = _utc_now()
 
         # Auto-generate title from first user message if not set
         if not conversation.title and role == "user":
diff --git a/server/services/scheduler_service.py b/server/services/scheduler_service.py
index d6fc1b6..eb22a3a 100644
--- a/server/services/scheduler_service.py
+++ b/server/services/scheduler_service.py
@@ -368,6 +368,14 @@ class SchedulerService:
             logger.info(f"Agent already running for {project_name}, skipping scheduled start")
             return
 
+        # Register crash callback to enable auto-restart during scheduled windows
+        async def on_status_change(status: str):
+            if status == "crashed":
+                logger.info(f"Crash detected for {project_name}, attempting recovery")
+                await self.handle_crash_during_window(project_name, project_dir)
+
+        manager.add_status_callback(on_status_change)
+
         logger.info(
             f"Starting agent for {project_name} "
             f"(schedule {schedule.id}, yolo={schedule.yolo_mode}, concurrency={schedule.max_concurrency})"
@@ -382,6 +390,8 @@ class SchedulerService:
             logger.info(f"✓ Agent started successfully for {project_name}")
         else:
             logger.error(f"✗ Failed to start agent for {project_name}: {msg}")
+            # Remove callback if start failed
+            manager.remove_status_callback(on_status_change)
 
     async def _stop_agent(self, project_name: str, project_dir: Path):
         """Stop the agent for a project."""
@@ -457,7 +467,10 @@ class SchedulerService:
     def _create_override_for_active_schedules(
         self, project_name: str, project_dir: Path, override_type: str
     ):
-        """Create overrides for all active schedule windows."""
+        """Create overrides for all active schedule windows.
+
+        Uses atomic delete-then-create pattern to prevent race conditions.
+        """
         from api.database import Schedule, ScheduleOverride, create_database
 
         try:
@@ -479,17 +492,20 @@ class SchedulerService:
                     # Calculate window end time
                     window_end = self._calculate_window_end(schedule, now)
 
-                    # Check if override already exists
-                    existing = db.query(ScheduleOverride).filter(
+                    # Atomic operation: delete any existing overrides of this type
+                    # and create a new one in the same transaction
+                    deleted = db.query(ScheduleOverride).filter(
                         ScheduleOverride.schedule_id == schedule.id,
                         ScheduleOverride.override_type == override_type,
-                        ScheduleOverride.expires_at > now,
-                    ).first()
+                    ).delete()
 
-                    if existing:
-                        continue
+                    if deleted:
+                        logger.debug(
+                            f"Removed {deleted} existing '{override_type}' override(s) "
+                            f"for schedule {schedule.id}"
+                        )
 
-                    # Create override
+                    # Create new override
                     override = ScheduleOverride(
                         schedule_id=schedule.id,
                         override_type=override_type,
diff --git a/ui/src/components/ScheduleModal.tsx b/ui/src/components/ScheduleModal.tsx
index 0d54865..8c412a5 100644
--- a/ui/src/components/ScheduleModal.tsx
+++ b/ui/src/components/ScheduleModal.tsx
@@ -14,8 +14,9 @@ import {
   useToggleSchedule,
 } from '../hooks/useSchedules'
 import {
-  utcToLocal,
-  localToUTC,
+  utcToLocalWithDayShift,
+  localToUTCWithDayShift,
+  adjustDaysForDayShift,
   formatDuration,
   DAYS,
   isDayActive,
@@ -109,10 +110,18 @@ export function ScheduleModal({ projectName, isOpen, onClose }: ScheduleModalPro
         return
       }
 
-      // Convert local time to UTC
+      // Convert local time to UTC and get day shift
+      const { time: utcTime, dayShift } = localToUTCWithDayShift(newSchedule.start_time)
+
+      // Adjust days_of_week based on day shift
+      // If UTC is on the next day (dayShift = 1), shift days forward
+      // If UTC is on the previous day (dayShift = -1), shift days backward
+      const adjustedDays = adjustDaysForDayShift(newSchedule.days_of_week, dayShift)
+
       const scheduleToCreate = {
         ...newSchedule,
-        start_time: localToUTC(newSchedule.start_time),
+        start_time: utcTime,
+        days_of_week: adjustedDays,
       }
 
       await createSchedule.mutateAsync(scheduleToCreate)
@@ -203,8 +212,12 @@ export function ScheduleModal({ projectName, isOpen, onClose }: ScheduleModalPro
         {!isLoading && schedules.length > 0 && (
           <div className="space-y-3 mb-6 max-h-[300px] overflow-y-auto">
             {schedules.map((schedule) => {
-              const localTime = utcToLocal(schedule.start_time)
+              // Convert UTC time to local and get day shift for display
+              const { time: localTime, dayShift } = utcToLocalWithDayShift(schedule.start_time)
               const duration = formatDuration(schedule.duration_minutes)
+              // Adjust displayed days: if local is next day (dayShift=1), shift forward
+              // if local is prev day (dayShift=-1), shift backward
+              const displayDays = adjustDaysForDayShift(schedule.days_of_week, dayShift)
 
               return (
                 <div
@@ -223,7 +236,7 @@ export function ScheduleModal({ projectName, isOpen, onClose }: ScheduleModalPro
                     {/* Days */}
                     <div className="flex gap-1 mb-2">
                       {DAYS.map((day) => {
-                        const isActive = isDayActive(schedule.days_of_week, day.bit)
+                        const isActive = isDayActive(displayDays, day.bit)
                         return (
                           <span
                             key={day.label}
diff --git a/ui/src/lib/timeUtils.ts b/ui/src/lib/timeUtils.ts
index 036c171..5dad704 100644
--- a/ui/src/lib/timeUtils.ts
+++ b/ui/src/lib/timeUtils.ts
@@ -4,38 +4,135 @@
  *
  * Utilities for converting between UTC and local time for schedule management.
  * All times in the database are stored in UTC and displayed in the user's local timezone.
+ *
+ * IMPORTANT: When converting times, day boundaries may be crossed. For example:
+ * - Tokyo (UTC+9) user sets 02:00 local → 17:00 UTC previous day
+ * - New York (UTC-5) user sets 22:00 local → 03:00 UTC next day
+ *
+ * The days_of_week bitfield must be adjusted accordingly using shiftDaysForward/shiftDaysBackward.
  */
 
+/**
+ * Result of time conversion including day shift information.
+ */
+export interface TimeConversionResult {
+  time: string
+  dayShift: -1 | 0 | 1 // -1 = previous day, 0 = same day, 1 = next day
+}
+
 /**
  * Convert "HH:MM" UTC time to user's local time.
  * @param utcTime Time string in "HH:MM" format (UTC)
- * @returns Time string in "HH:MM" format (local)
+ * @returns Object with local time string and day shift indicator
  */
-export function utcToLocal(utcTime: string): string {
+export function utcToLocalWithDayShift(utcTime: string): TimeConversionResult {
   const [hours, minutes] = utcTime.split(':').map(Number)
-  const utcDate = new Date()
-  utcDate.setUTCHours(hours, minutes, 0, 0)
+
+  // Use a fixed reference date to calculate the shift
+  const utcDate = new Date(Date.UTC(2000, 0, 15, hours, minutes, 0, 0)) // Jan 15, 2000
+  const localDay = utcDate.getDate()
+
+  let dayShift: -1 | 0 | 1 = 0
+  if (localDay === 14) dayShift = -1 // Went to previous day
+  if (localDay === 16) dayShift = 1 // Went to next day
 
   const localHours = utcDate.getHours()
   const localMinutes = utcDate.getMinutes()
 
-  return `${String(localHours).padStart(2, '0')}:${String(localMinutes).padStart(2, '0')}`
+  return {
+    time: `${String(localHours).padStart(2, '0')}:${String(localMinutes).padStart(2, '0')}`,
+    dayShift,
+  }
+}
+
+/**
+ * Convert "HH:MM" UTC time to user's local time (legacy function for backwards compatibility).
+ * @param utcTime Time string in "HH:MM" format (UTC)
+ * @returns Time string in "HH:MM" format (local)
+ */
+export function utcToLocal(utcTime: string): string {
+  return utcToLocalWithDayShift(utcTime).time
 }
 
 /**
  * Convert "HH:MM" local time to UTC for storage.
  * @param localTime Time string in "HH:MM" format (local)
- * @returns Time string in "HH:MM" format (UTC)
+ * @returns Object with UTC time string and day shift indicator
  */
-export function localToUTC(localTime: string): string {
+export function localToUTCWithDayShift(localTime: string): TimeConversionResult {
   const [hours, minutes] = localTime.split(':').map(Number)
-  const localDate = new Date()
-  localDate.setHours(hours, minutes, 0, 0)
+
+  // Use a fixed reference date to calculate the shift
+  // Set local time on Jan 15, then check UTC date
+  const localDate = new Date(2000, 0, 15, hours, minutes, 0, 0) // Jan 15, 2000 local
+  const utcDay = localDate.getUTCDate()
+
+  let dayShift: -1 | 0 | 1 = 0
+  if (utcDay === 14) dayShift = -1 // UTC is previous day
+  if (utcDay === 16) dayShift = 1 // UTC is next day
 
   const utcHours = localDate.getUTCHours()
   const utcMinutes = localDate.getUTCMinutes()
 
-  return `${String(utcHours).padStart(2, '0')}:${String(utcMinutes).padStart(2, '0')}`
+  return {
+    time: `${String(utcHours).padStart(2, '0')}:${String(utcMinutes).padStart(2, '0')}`,
+    dayShift,
+  }
+}
+
+/**
+ * Convert "HH:MM" local time to UTC for storage (legacy function for backwards compatibility).
+ * @param localTime Time string in "HH:MM" format (local)
+ * @returns Time string in "HH:MM" format (UTC)
+ */
+export function localToUTC(localTime: string): string {
+  return localToUTCWithDayShift(localTime).time
+}
+
+/**
+ * Shift days_of_week bitfield forward by one day.
+ * Used when UTC time is on the next day relative to local time.
+ * Example: Mon(1) -> Tue(2), Sun(64) -> Mon(1)
+ */
+export function shiftDaysForward(bitfield: number): number {
+  let shifted = 0
+  if (bitfield & 1) shifted |= 2 // Mon -> Tue
+  if (bitfield & 2) shifted |= 4 // Tue -> Wed
+  if (bitfield & 4) shifted |= 8 // Wed -> Thu
+  if (bitfield & 8) shifted |= 16 // Thu -> Fri
+  if (bitfield & 16) shifted |= 32 // Fri -> Sat
+  if (bitfield & 32) shifted |= 64 // Sat -> Sun
+  if (bitfield & 64) shifted |= 1 // Sun -> Mon
+  return shifted
+}
+
+/**
+ * Shift days_of_week bitfield backward by one day.
+ * Used when UTC time is on the previous day relative to local time.
+ * Example: Tue(2) -> Mon(1), Mon(1) -> Sun(64)
+ */
+export function shiftDaysBackward(bitfield: number): number {
+  let shifted = 0
+  if (bitfield & 1) shifted |= 64 // Mon -> Sun
+  if (bitfield & 2) shifted |= 1 // Tue -> Mon
+  if (bitfield & 4) shifted |= 2 // Wed -> Tue
+  if (bitfield & 8) shifted |= 4 // Thu -> Wed
+  if (bitfield & 16) shifted |= 8 // Fri -> Thu
+  if (bitfield & 32) shifted |= 16 // Sat -> Fri
+  if (bitfield & 64) shifted |= 32 // Sun -> Sat
+  return shifted
+}
+
+/**
+ * Adjust days_of_week bitfield based on day shift from time conversion.
+ * @param bitfield Original days_of_week bitfield
+ * @param dayShift Day shift from time conversion (-1, 0, or 1)
+ * @returns Adjusted bitfield
+ */
+export function adjustDaysForDayShift(bitfield: number, dayShift: -1 | 0 | 1): number {
+  if (dayShift === 1) return shiftDaysForward(bitfield)
+  if (dayShift === -1) return shiftDaysBackward(bitfield)
+  return bitfield
 }
 
 /**