I've noticed the same thing myself at various times in my life. My most frequent sleep schedule I maintained was 4am to noon, but it drifts from that pretty often. And when it does, my days push longer. I actually mapped out a "6 day week," where I would sleep 8 hours and be up 20. It lines up with a 24/7 week where I wake up at the same time on the same day each week.

Thank you for posting this. It's encouraging me to consider giving that a shot again. (especially since I woke up at 5pm and that's been pushing later again)