Figure out whether your circadian time is set for early morning (~5AM wake up time), day (~10AM wake), or night (~2PM wake). Despite what most people think, it's incredibly hard for one type to adapt to another.
Scientifically? No clue. But I figured out I was a night owl by the sheer fact that going to sleep at 5-6 AM to wake up at 12-2PM makes me feel well rested, whereas literally no amount of sleep will make me feel well rested if I have to wake up at 7-8.
I visited the U.S. back in 2019, and I recall that no matter how late I went to bed, in the U.S. I was awake and alert at 6AM, almost on the dot. It was so weird being a morning person for the first time in my life, since my country is 6 hours ahead of where I visited, meaning here I would've gotten up at noon.
I know that mine is a night one because I worked evening/nights for like 10 years and felt great. I've been working a 9-5 for about 4 years now and have learned to pretend I'm functioning on about 4 hours sleep per night. Sucks.