Night as in 10pm-3am
That being said, I also take a day off, an afternoon off, etc. just to keep myself from burning out.
Some people don't work well in a routine manner. Startups are so dynamic too, so if you're in that realm of things, it's almost impossible to have a routine schedule.
Going to bed every night, knowing you won't have to wakeup for 8 hours, is really comforting. I usually wakeup before my timer goes off, but it's way better sleep.
Unfortunately this can't always happen, especially with meetings and such.
On the weekend I tend to be most productive between 9am and 12pm (if the wife's still in bed), but I don't really gear up till between 2pm and 7pm.
My most productive time is usually after lunch as my mornings are usually filled with meetings, phone calls and emails. Evenings I work on my own projects and freelance. I'm more enthused about the work but find there are more distractions as well.