diff --git a/src/memos/mem_scheduler/base_scheduler.py b/src/memos/mem_scheduler/base_scheduler.py
index 5720939e0..62e1d0242 100644
--- a/src/memos/mem_scheduler/base_scheduler.py
+++ b/src/memos/mem_scheduler/base_scheduler.py
@@ -785,7 +785,8 @@ def _message_consumer(self) -> None:
                         if enqueue_epoch is not None:
                             queue_wait_ms = max(0.0, now - enqueue_epoch) * 1000
 
-                        msg.dequeue_ts = now
+                        # Avoid pydantic attribute enforcement
+                        object.__setattr__(msg, "_dequeue_ts", now)
                         emit_monitor_event(
                             "dequeue",
                             msg,
diff --git a/src/memos/mem_scheduler/task_schedule_modules/dispatcher.py b/src/memos/mem_scheduler/task_schedule_modules/dispatcher.py
index a2d01df6b..ade2bbfbf 100644
--- a/src/memos/mem_scheduler/task_schedule_modules/dispatcher.py
+++ b/src/memos/mem_scheduler/task_schedule_modules/dispatcher.py
@@ -166,7 +166,7 @@ def wrapped_handler(messages: list[ScheduleMessageItem]):
                 wait_sec = max(0.0, now - enq_epoch)
                 self.metrics.observe_task_wait_duration(wait_sec, m.user_id, m.label)
 
-                dequeue_ts = getattr(first_msg, "dequeue_ts", None)
+                dequeue_ts = getattr(first_msg, "_dequeue_ts", None)
                 start_delay_ms = None
                 if isinstance(dequeue_ts, int | float):
                     start_delay_ms = max(0.0, start_time - dequeue_ts) * 1000