Refactor: keep timestamp consistency (#12279)

### What problem does this PR solve?

keep timestamp consistency

### Type of change

- [x] Refactoring

api/db/services/evaluation_service.py

@@ -65,6 +65,7 @@ class EvaluationService(CommonService):
             (success, dataset_id or error_message)
         """
         try:
+            timestamp= current_timestamp()
             dataset_id = get_uuid()
             dataset = {
                 "id": dataset_id,
@@ -73,8 +74,8 @@ class EvaluationService(CommonService):
                 "description": description,
                 "kb_ids": kb_ids,
                 "created_by": user_id,
-                "create_time": current_timestamp(),
-                "update_time": current_timestamp(),
+                "create_time": timestamp,
+                "update_time": timestamp,
                 "status": StatusEnum.VALID.value
             }