For over a decade now, I am fortunate enough to just let my body decide, so I go to sleep whenever I feel like I want to sleep and wake up whenever it happens…
Hours are funny tho, middle point is probably somewhere around 6, sometimes there are times when it is closer to 4, and less often but it happens, around 8.
From my observations and whenever I talk with anyone invested in their routines, it mostly boils down to quality over quantity. Shitty 9 or 10 hours might feel terribly unpleasant and 30 min power nap can do wonders sometimes.
I always believed to be the night owl until I discovered it can switch for me and then I figured out a new option of being a morning lark — I must say, both have some benefits actually but the whole day timetable changes dramatically.