[Bug fix] need record start time in pd mode (#5425)

python/sglang/srt/managers/scheduler.py

@@ -959,14 +959,12 @@ class Scheduler(
             self._add_request_to_queue(req)
 
     def _add_request_to_queue(self, req: Req):
+        req.queue_time_start = time.time()
         if self.disaggregation_mode == DisaggregationMode.PREFILL:
             self.disagg_prefill_pending_queue.add(req)
-
         elif self.disaggregation_mode == DisaggregationMode.DECODE:
             self.disagg_decode_prealloc_queue.add(req)
-
         else:
-            req.queue_time_start = time.time()
             self.waiting_queue.append(req)
 
     def _extend_requests_to_queue(self, reqs: List[Req], is_retracted: bool = False):