Uhm... rrrrrrrright!!!!

[Enigma]

For years I was a railwayman on shiftwork and I had enormous trouble getting up at 3 and 4 in the morning to go to work. Often late as a consequence. I always had 3 hours of an afternoon to compensate. No trouble with late shift as I would not rise untill 11am.

Now I am retired I find I am awake at 4 in the morning and have to have an afternoon nap. I never sleep now for more than 4 hours at a stretch anyway. So I suppose it is what your internal clock gets used to in the long run.