just a pilot but..
Depends on what equipment you are on. Dare say they expect the 320/73 guys to be pretty accurate (GPS Clocks).
I try as hard as I can to meet their request and if it looks as though I can't let them know. It kills the fuel savings and is annoying when they give it to you 1 second after top of descent. I do try to keep in mind how understaffed they are and thus don't ever complain.
Find most are quite appreciative if you help however/wherever you can.