When I was working I rose every morning at 6.30 - no alarm, just a natural internal clock. (When we had the dog, it started at 6am...).

That routine lasted for 30+ years or so. I thought that, when I retired, I'd be unable to break the habit. Bugger me, on the first day of my retirement, I woke quite happily at 9! And between 8 and 9 has been the pattern for the last 6 years.