This is the kind of anecdotal response I was referring to with my statement. While I agree that you can shift your rhythm by a couple of hours, that does not me

This is the kind of anecdotal response I was referring to with my statement. While I agree that you can shift your rhythm by a couple of hours, that does not mean standing up at 6:30 will ever be natural for me. Against your anecdote, I present myself starring at the ceiling (which is torture for me, I can not shut off my brain, ever.) for many many school years to no effect. I did try many things, because it's certainly not fun to feel tired all the time. But if left to my own devices I get into a 3am-11am rhythm and have worked like this in my adulthood for multiple years. I can rather easily shift by 2 hours to a 1am to 9am rhythm without much impact, I do feel the impact (tiredness, hard to fall asleep) of a 3 hour shift from midnight to 8am and I'm absolutly unable to go to bed at 10:30 so I can be rested at 6:30. Even if I manage to fall asleep that soon (e.g. from physical exhaustion), I will not be rested at all when standing up at 6:30. Interesting enough, I can also shift my rhythm by a similar amount in the other direction. A lot of my social life happens online and when I was spending 6 months in a timezone 7 hours shifted from my local friends, I could shift my rhythm to go to bed between 5 and 6am so I have more overlapping online-time with them, but I couldn't shift it further. So, how is your response not ignorance of a different rhythm?