It varies. I wakeup around 9am each morning without an alarm no matter what time I go to bed. I try to be in bed by 1am, but if I stay up until 4am I still wakeup naturally around 9. Sometimes I can go back to sleep for another hour and a half or so though if I stayed up really late.

I feel the same with 6-9 hours of sleep. Any less and I notice it though.