I had the opposite experience a few years ago, I am very much a night owl.

I did a job that required me in the office for 7am for a few months, I was noticeably less effective for the whole duration, I was just slower at everything and was basically constantly tired. Switched back to getting in for 9-10am and the difference was night and day, as basically I was back to my old levels of effectiveness after a day or two.

I just think I'm one of these people that cannot adapt, or at least if I do, it comes with a cost.

I'm a night owl and even early morning acclimatization hasn't helped.

There were a few months that I had to do 12.5 hour shift work where I had to be at work at 5:30 AM and I was miserable the entire time. It's hard to adjust when your natural cycle is like 10 am to 2 am.

I've done all the shifts and it fucking sucks.

We did week about shifts. That meant earlies for a week, nights, then lates. Every week you had to change your sleep pattern.

I liked earlies to nights because long weekend (finish 11am Fri start 10am Mon) and a fun "adaptation" that required me to stay up as late as I possibly could on Sunday night. I'd drink, smoke and play games with US chums (UK here) until 3 or 4am and then sleep as late as possible.

It fucking sucked but I did it for a good decade. Then managed to wangle permanent 6-2 shift.

It was a revelation.

Suddenly I had a regular sleep pattern. It was hard to train, but I managed to get a good 6 hours a night most nights. Which was good, I've always suffered insomnia for lots of reasons, so I managed to become one of those people that survives on minimal sleep. More sleep was amazing.

I've kind of got it down nowadays, thanks in no small part to some pills I was given for my restless legs. They make me drowsy, so if I take them at the right time I can force a sleep pattern, and they stop me kicking my wife up the arse when I'm asleep.

Back to your point after a trip through the weeds, I now do 2 week late shift and 2 week early shift, there's a permanent night shift at this new place.

When I'm on the early shift I wake up at 5am on the Saturday and Sunday without fail. Once I forgot to set my alarm for work and woke up a minute before it should have gone off. Years of the early shift have honed my wake up time to a knife edge.

Sometimes on the weekend I can't get back to sleep for various reasons, so it's not an uncommon sight to find me gaming on my PC at 7am on a Sunday morning. I don't want to be there, but it's kinda nice having the peace and quiet of being a night owl with the sun up and a sleep cycle behind instead of in front of you.