To the OP's original question, I get about 7 hours.
Problem is, my timing is so fucked up. Yesterday I went to bed at 7am and work up at 2pm. Back in the day I didn't mind this as I could work well at night. Maybe it's cause I'm older now, but I really do enjoy being up in the morning and seizing the day. I want to try for 12am to 7am.