diff --git a/src/baby_monitor/models/sleep.py b/src/baby_monitor/models/sleep.py
index 2a48251..2550ca2 100644
--- a/src/baby_monitor/models/sleep.py
+++ b/src/baby_monitor/models/sleep.py
@@ -15,6 +15,7 @@ class CreateSleepRequest(BaseModel):
 class UpdateSleepRequest(BaseModel):
     """Request model for updating a sleep log."""
 
+    start_time: datetime | None = None
     end_time: datetime | None = None
 
 
diff --git a/src/baby_monitor/repositories/interfaces/sleep_repository_interface.py b/src/baby_monitor/repositories/interfaces/sleep_repository_interface.py
index 655af76..75c6922 100644
--- a/src/baby_monitor/repositories/interfaces/sleep_repository_interface.py
+++ b/src/baby_monitor/repositories/interfaces/sleep_repository_interface.py
@@ -32,6 +32,7 @@ class SleepRepositoryInterface(ABC):
     def update(
         self,
         sleep_id: int,
+        start_time: datetime | None = None,
         end_time: datetime | None = None,
     ) -> dict | None:
         """Update a sleep log entry."""
diff --git a/src/baby_monitor/repositories/sleep/sqlite_sleep.py b/src/baby_monitor/repositories/sleep/sqlite_sleep.py
index 819c47d..43826aa 100644
--- a/src/baby_monitor/repositories/sleep/sqlite_sleep.py
+++ b/src/baby_monitor/repositories/sleep/sqlite_sleep.py
@@ -73,6 +73,7 @@ class DatabaseSleepRepository(SleepRepositoryInterface):
     def update(
         self,
         sleep_id: int,
+        start_time: datetime | None = None,
         end_time: datetime | None = None,
     ) -> dict | None:
         """Update a sleep log entry."""
@@ -80,6 +81,8 @@ class DatabaseSleepRepository(SleepRepositoryInterface):
         if not sleep:
             return None
 
+        if start_time is not None:
+            sleep.start_time = start_time  # type: ignore[assignment]
         if end_time is not None:
             sleep.end_time = end_time  # type: ignore[assignment]
 
diff --git a/src/baby_monitor/routers/sleep.py b/src/baby_monitor/routers/sleep.py
index 7f6f1c6..a4ba414 100644
--- a/src/baby_monitor/routers/sleep.py
+++ b/src/baby_monitor/routers/sleep.py
@@ -112,6 +112,7 @@ def update_sleep(
 
     updated = sleep_repo.update(
         sleep_id=sleep_id,
+        start_time=request.start_time,
         end_time=request.end_time,
     )