I regulate my sleep on week days to 6 hours. That is all I need for maximum concentration in the working days... I don't have a limit on weekends, and will usually stay up until about 3-4 and then get up about 10... so strangly still getting 6 hours... :/ And I have only just realised that as I typed!
0100 is my bed time on a work night, as I get up at 0700!
0100 is my bed time on a work night, as I get up at 0700!