Apparently, many many decades ago, people used to go to bed until maybe 2-3am then get up and visit friends, family, neighbours and make love (or any permutation) They would then go back to bed and sleep for another few hours.
THAT is the true cycle of sleep. It comes in waves.
I can sleep for England and have no qualms or guilt about reading in the afternoon either outdoors in good weather or on the bed if too hot, with a fan on, windows open, shutters closed, waking up to find it's 5 or 6pm.
Still, that's one luxury of being retired.
Normally bed around 11pm, read, sleep and wake around 6-7am.
I do occasionally wake around 3am and make tea which I take back to bed. I also keep tabs on my sleeping and eating habits, BP, heart-rate, stress and oxygen levels via the Samsung Health app which is pre-loaded. I find it handy in that it keeps graphs of your health history.