The risk with an inconsistent waking time is shifting forward the circadian rhythm, if you sleep in later and later. When that occurs you'll fall asleep later as well, or wake up more often. A wind-down period ahead of bedtime can also offer some flexibility, if you happen to have enough sleep pressure to fall asleep earlier some nights.
I countered this by setting a go to sleep alarm. Alarm goes off, time to wind it up and head to bed. I do have a morning alarm (multiple of them) but I've been waking up before they go off.
Yeah I basically schedule time before bed. What people take for granted is that an increasingly fatigued state can also lead you to procrastinate on sleep, i.e. if you're tired and dicking around on electronics mindlessly, you'll just keep doing it and have trouble pulling yourself away. Whereas if I just read a book that's no trouble.
When I stop using alarms and stop forcing myself to go to sleep early, my hours seem to converge to something very similar to yours. I experience the "shifting forward" until I get to 2am-11am, and the shifting stops.
I've noticed the same pattern on roommates and family members as well.
Doesn't seem necessary, but at any rate only a small dose is needed to be effective i.e. 0.3mg. Too much OTC melatonin can backfire and lead to grogginess.
Melatonin levels should naturally spike near onset, but it can be suppressed by blue light emitting electronics and caffeine. A filter like flux on media devices in the evening can help - https://justgetflux.com/
