Typically around 04:00-12:00 for me. Fortunately, I have a job that fits nicely around that, so I'm in a pretty good place overall, but when I do have to try to shift to more "normal" schedules it really wreaks havoc on my energy levels and mental clarity.
I've tried all sorts in an attempt to make a "normal" schedule work for me, like sleep monitoring, therapy, sleeping pills, and just being really over-the-top about my sleep hygiene (like not allowing screen usage for X hours before bed, no drinking or eating X hours before bed, etc). I can sort of make a "normal" schedule stick but I never feel good for it. And it takes constant work because my body naturally wants to gradually drift back towards a 4am sleep time, and I find going to sleep earlier than previous nights very difficult so once it starts slipping it usually takes an all-nighter to get it back to where I want it.
Like I said, I've generally got things pretty good right now with my job and lifestyle working around my sleep schedule. But it'd certainly be a lot easier if society didn't think I was lazy and was able to accommodate me (and other people with less "normal" sleep schedules) a little more.