"Catching up" on sleep takes one to two weeks.
We've all justified our bad sleeping patterns with something like "oh, it's fine, I'll catch up on the weekend." While it seems reasonable at first, it's actually close to impossible. While a week of all-nighters will catch up to you by the weekend, and you might sleep those precious two days away, you actually are not catching up like you might think. In fact, you might be making the situation even worse by confusing your internal clock.
In order to truly catch up on sleep, you have to reestablish and maintain a regular pattern, as well as recover from the fatigue that a former irregular pattern may have caused. How long does this take? At least one week, sometimes even two. So, if you are considering going out partying and figure that it won't affect that meeting that's in a few days, that you'll catch up in between... think again.