It so much depends on the precision of the job. Is it paramount to finish on time? Is the job to stop in-process when time is running out? Or is it rather unimportant?

Imagine your boss is coming round telling you to manually stamp envelopes for the next two hours. No reprogramming any printers, hands off the keyboard. Take that stamp and stamp away.

So you stamp an envelope each and then look at the clock or your watch, check the two hours haven't passed yet and proceed?

Or you absentmindedly stamp away, always fixing the clock with your eyes and let the stamp fly out of your hands when time's finally out?

In programming, you could calculate the time when to stop, create a sub stampit and a loop checking for the time out to be reached around calling that subroutine... in the first place. In the second, also check for the time inside the stamping routine and when time's out, leave it (i.e. return to end the loop) with the last; command.

Cheers, Sören