Do you find your sleep skews? Any longer (2-3 week) vacations I've taken I've found that my waking up time keeps skewing even if I'm not going to bed later. Maybe I've never seen the end where it stabilizes.
My sleep cycle naturally drifts infinitely by some 30 minutes a day on average.
It makes life strange at times, especially on this latitude. Imagine waking up at night through a whole winter, not seeing the Sun for months.
I've tried to hold steady cycle but I just grow more and more tired every day until finally the alarm fails to wake me. School was hell. Was absent a lot simply for sleeping.
Pre-pandemic we were all waking around 8am to get my daughter to pre-school. Within a week of foregoing bedtimes, we were all going to bed between 2am and 4am and waking up around 11am. So the kids still got their 9 hours and the adults got their 7, but it did stabilize.
Sometimes I want to sleep a few extra hours. Sometimes I'm so excited for the day, I get up early and go to sleep late. Sometimes I need to stay up for a while, and next time I sleep it's for 20 hours straight. Sometimes it's just a nap here and there for a few days.
The most important thing I've learned is to listen to my tiredness level, and not get too carried away with productivity.
When I was in college I'd pretty quickly drift to a 4:00AM to noon sleep schedule on holidays. Even today (in my mid 20's) I find I'm happiest sleeping from roughly 2:00AM to 10:00AM.