Music playlists: 30min, 60min, 90min, 2hr etc
9 times out of 10 if it does go over a little it's because I allowed it.
Also I have kind of an internal clock....i've done this just long enough I have a pretty good sense of how much time has passed.
Technically I think the one who should be SLIGHTLY more responsible about the time though is the client. Responsibility is about 60/40. Since we're not supposed to be clockwatchers but a good client isn't supposed to take advantage.