It has long TAT at HWH so generally it is not rescheduled unless incoming train is late by at least 5-6 hrs, which is rare in summer. 12311 mostly remains on time till DDU and gets slightly late near CNB but again uses the slack before DLI to arrive on time at DLI and KLK. 12312 is less punctual but generally it is only 2-3 hrs late, which is OK on IR for a mail train on GC route.