Agree with zac08. Even when it sounds the same to you (waking up for 2 hours during night time, and taking 2 hours of date time to rest), it is not the same.

I, for example, hate it at work when they sometime ask us to stay late, even when that also means coming late, cause that is not our supposed working hour. They may say, come 2 hours late, but because of my internal clock, I would be up at my regular time. And coming home 2 hours late from work, really can make lot of difference in long term.