Whenever I need to get something done. OK ... I admit to being lazy.
Other than that my only "sort of" steady hours is 9am to maybe 11-11:30am 3 or 4 days during week when I do my daytrading gig.
When summertime comes around and the patios are open, I'm in "kick back" mode.
Flexibility is what I strived for all these years. I'm fortunate that I'm able to have that flexibility nowadays.