You are right. But, there is always 17404 at Bhimavaram Town which can't be delayed. If Circar is rescheduled to depart late by another 25 minutes, then it would reach BVRT around 18:10 - add 15 - 20 minutes delay to that. Thus, it will clash with 17404. Besides, it will further delay BVRT-NDD passenger which is connecting train to 57231. Circar cannot follow 17404 because PF3 in GDV is blocked by 7402, PF1 by 7404 and PF2 will be blocked for 7480/7482. Hence, it is not a viable option to pospone the departure by 25 minutes at COA unless 7404's schedule is adjusted which I think is too tough to happen.