What time did the woman go to bed?

Woman: I’m exhausted. I didn’t get to bed last night until after eleven.
Man: Really? That’s not so late, not unless you got up very early, of course.
Woman: I did get up early. I got up at four. I usually get eight hours of sleep, but last night I got only five. That’s not enough for me.
Man: No, that wouldn’t be enough for me, either. Why did you get up so early? Were you getting ready for a trip or something?
Woman: No, I wanted to get to the office early because I had some extra work to finish. Even though it means getting up in the dark, I’d rather do that than stay at the office until late at night.