I tend to believe your “internal clock” becomes more accurate the longer you live. In my 20s I could be off by an hour easy. In my 30s kinda got refined just by waking up a few minutes before the alarm clock, so I didn’t have to listen to the damn thing. In my 40s I can wake up from a dead sleep in the middle of the night and guess what time it is within a matter of a few minutes. Sorry for droning on. Just an observation. :), amirite?