If you stay up late and you have another hour of work to do, you can just stay up another hour later without running into a wall and having to stop. Whereas it might take three or four hours if you start over, you might finish if you just work that extra hour. If you're a morning person, the day always intrudes a fixed amount of time in the future. So it's much less efficient. Which is why I think computer people tend to be night people - because a machine doesn't get sleepy.