I go to bed at three or four am, get up around seven am average. Sleeping more/later or napping will inevitably make me more tired.
The most sleep I need to function is three hours, but I try for five at least so I won't be dead the next day.
If there's any light at all I can't sleep. I've slept through fire alarms but wake up if a door creaks.
I think all this is stuff I've made myself do just not to waste any hours, but like people have said, I rarely do anything during these hours. I did stay awake for two days once, just to try it, and was surprised at how easy it was for me.