My sleeping habits are irreparably smurfed, so I'm always up late whether I'm getting up at 8 am for class or in the afternoon because I've got the day off. And I take naps.

But more to the point, night is the time to be awake. The temperature is much better, everything's calmer and quieter, and most people are asleep. I don't rely on caffeine or anything to keep me awake. If I'm too tired to stay up on my own, I just go to sleep.