Now that I am in my mid-60s and not going out to work any longer, I find that my sleep pattern is becoming increasingly odd!
Typically, I go to bed between 02:30 and 04:00 and get to sleep between 03:30 and 05:00. If I didn't have anything planned the next day I would wake up between 10:00 and 10:30 so that would be five to seven hours sleep. (If I have guests, it would be more like 09:00 to 09:30.)
If I have a blood test (usually at 08:45) I would get up at about 08:00 no matter what time I went to sleep.
If I had to leave home at 09:00 for a long bike ride, I'd get up at 07:00 (even if I'd only had three or four hours sleep) because I like to eat a big breakfast two hours before setting off.
If I am out doing things all day then I don't feel too bad from lack of sleep, but if I am working on my laptop at home then I always doze off a couple of times in the afternoon. If I didn't have a nap in the afternoon then I would have one in the evening after eating.
If I went to bed very late, got up for an early breakfast, went out early for an all-day ride, got home at (say) 23:00 without having had the chance to have a nap at any point in the day then I'd have a quick shower, something to eat, and probably start to flag a little by midnight so I'd be in bed by 00:30 and probably asleep by 01:00. But then I might wake up after five or six hours, play a couple of games of Sudoku/Spider Solitaire/(whatever) on my tablet and go back to sleep again when I could no longer concentrate.
Hmm, here's a coincidence... I was drawn to this thread by the title, not being aware of what biphasic sleeping is, then I went off to check the news on the BBC website and found
THIS!