It's nice to wake up at 6am. or 5am. or even 4am. if that schedule optimizes your daily accomplishments.

It is also nice to wake up at 7am. or 8am. if that schedule is required to rest your brain from the previous day's firing of all those neurons.

The time you go to bed also counts, and different people require different number of hours of sleep to get ready at peak level for the day.