Too bad: -M (see perldoc -f -X) does just that except that it's in days, not seconds. So one has to backconvert. Half-heartedly I think that maybe it may have been more convenient to stick with seconds, but I'm not really sure...

Oh, and of course -M compares with script startup time, not time(), which may be a completely negligible difference or a very relevant one depending on the actual application!

Well, it just to give the OP another option...