Government Employees upto BS-18 do get late sitting. Its a nominal amount, if you have stayed in office after 3 hours of Office Timing i.e. till 7 P.M. in Federal Secretariat.
However, as a CSP you need to work late at nights casually. The Joint Secretary of our Ministry is a DMG officer, who sits daily till, at least, 8
0 P.M. Though no benefit for him (since he is in BS-20), yet his staff does get late sitting, nonetheless they are not happy with their Boss...
Sitting late to perform official duties of diverse nature, that may or may not come under your designated work (distribution of work) may give you a place of prominence to the high ups. Such bright officers do get Honorarium too, that is at least one basic pay (discretion of the Secretary) plus one more (with the permission of Chairman ECNEC)...
Regards