diff --git a/monitor.py b/monitor.py
index 2cad5cd..2a23e8d 100644
--- a/monitor.py
+++ b/monitor.py
@@ -966,17 +966,18 @@ class MessageHistory:
             conn.close()
 
     def get_latest_record_timestamp(self, platform: str) -> Optional[datetime]:
-        """获取该平台最近一条记录的时间戳（用于第二关判断）"""
-        self._ensure_ocr_staging_table()
+        """获取该平台最近一条记录的入库时间（用于第二关判断）"""
+        # ⭐ Task #1686: 查询 user_messages 表的 created_at 字段（入库时间）
+        self._ensure_user_messages_table()
         conn = self._get_conn()
         try:
             cursor = conn.execute(
-                "SELECT timestamp FROM ocr_staging WHERE platform=? ORDER BY timestamp DESC LIMIT 1",
+                "SELECT created_at FROM user_messages WHERE platform=? ORDER BY created_at DESC LIMIT 1",
                 (platform,)
             )
             row = cursor.fetchone()
             if row:
-                # timestamp 字段格式为 "YYYY-MM-DD HH:MM:SS"
+                # created_at 字段格式为 "YYYY-MM-DD HH:MM:SS"
                 try:
                     return datetime.strptime(row[0], "%Y-%m-%d %H:%M:%S")
                 except (ValueError, TypeError):