Jivraj, from my practical experience and a look at running status I can confirm that in case of trains which are running late, there are several instances where the train halts for a lesser duration than the scheduled time for stoppage at a station in order to make up for lost time to the extent possible. No passenger can complain in such a case because the train is departing from the station later than scheduled. Only instead of stopping for say 15 mns in a station like Vijayawada, it halts for 10 mns. There are numerous such instances, but with limitations. Say if the stoppage is for 15 mns the train does not however depart after a halt of say 2 mns.
However,...
more... the reverse is not true. If the train arrives at a station say 20 mns before time and has a stoppage there for 10 mns, it halts for 30 mns and departs only at the scheduled dep time so as to not inconvenience passengers who want to board at the last minute.