Like others, I was a night owl since my teenage years. I was also pretty sure my circadian rhythm was about a 28-hour cycle, so I'd go "out-of-phase" staying up

Like others, I was a night owl since my teenage years. I was also pretty sure my circadian rhythm was about a 28-hour cycle, so I'd go "out-of-phase" staying up later every day and sometimes skip or drastically shorten a night's sleep to get back in phase. However, it's now an effort to stay up past 10-10:30, and I wake up consistently around 6am. What changed? - 6 days/week with 6am meetings (remote work and timezones) - bright light (light box, much brighter than room lighting) and exercise early so I could function in those meetings - prioritized consistently going to bed and sleep early (often harder for me than getting up early) - and time passed post hoc, ergo propter hoc, but consistency with those habits made it easier to function in those mornings, and it got easier as time passed.