4:30am works best for me. I go to bed between 9 and 9:30pm almost every night. Occasionally it'll be later due to some event or catching up with people after which I'll still get up at 4:30am but it makes me significantly more tired. It's quick to fix though, I just go to bed even earlier the following night, around 8:15-8:30 does it best.

I know these times won't work for a lot of people but if you have young kids it's awesome. They're asleep anyway and working at night tends to ruin sleep for me so I just go to bed! Then the next morning I can work in peace without it disrupting my body so much.