I remember circadian rhythm... vaguely...

Years of submarine duty, with days of 18 hours / 24 hours / 30 hours, basically messed me up. Not working for those lengths, but that was the length of the day — because underwater, it was "whatever," and if I had one (or two) six-hour watches out of 18 hours I had an 18-hour day, essentially. "Breakfast" was "meal after waking" and whatever was on the menu was fine. Having the 00:00-06:00 and 06:00-12:00 watches with 12:00-24:00 off meant "breakfast" was "mid-rats" (subs serve four meals, one every six hours). And no sun to interfere with anything, of course.

The 30-hour "days" were the worst, IMHO. It was much easier to catch a few ZZZZs during a six-hour downtime than sleep 8+ hours during an 18-hour downtime. Fortunately those were rare.

On the plus side, even years later I have very little trouble with jet lag... 😁 If the sun is up, I'm up!