I have a pretty standard routine of: work/home/sleep/home/work, like most of us.
I awake, at about the same time, usually within a span of 10 minutes, every night, if my routine is on schedule.
I, and with using: “I”, I mean the shit that is running my brain, compensates for Daylight-Savings-Time within a week.
I eat some sort of candy/chocolate before bedtime, to ward off nightmares, so it could be a metabolism of sugars that completes around 3am, assuming my bedtime is met.
It is nothing new, I used to awake at 2am, on a daily basis, 20 years ago, and smile because I had at least 4 or 5 more hours of sleep. So it has been a lifelong thing.
Sometimes I will hit a “streak” where I wake up at like 3:08am for 6 days in a row. It has happened numerous times.
So how does a body-clock work? Kramer’s did, until the day of the race.