For me it depends on when I go to sleep. If I only get home from work at 8pm, it can a bit grim to go bed at 9.30 for a 5.30 start. But assuming I get home on time and get to bed on time, 5.30 is my preferred time.

That way I get to do some meditation, laze around reading the news, think through my calendar/next action lists and shower/groom/etc in a relaxed way rather than missing any out or rushing though.

There's also a practical benefit, which is that I ride my bike to work straight through Central London and its easier to do that before 8am, so I have to leave for work at just after 7.