Even this might be too simple.

The cicadean rhythm is synchronizing to the light of the sun, temperatures, when you eat, when you exercise and other kinds of routines, but what happens when we remove those?

Scientists in the 1960s set out to find out. From the late 1960 to early 1980s they put test subjects in a bunker. They found out that the human cycle is longer than 24 hours. The average might be around 25 hours, but not all. The longest was 50 hours. https://en.m.wikipedia.org/wiki/Bunker_experiment

Another well known experiment happened in 1989 where Stefania Follini was isolated in a cave for 4 months. Her internal clock went into a 48 hour cycle. https://en.m.wikipedia.org/wiki/Stefania_Follini

Of course these are extremes and not very useful knowledge for anyone who sees the sun daily or have actual stuff to do on a regular basis. However it shows that out sleep cycles are very much dependent on being synchronized to what we need to do.

Looking at people in hot places, who sleep (siesta) when it’s too hot outside, or people from non-industrial societies who might be active both during day and night and sleep in between, it’s pretty obvious that the 9-5 productive cycle is not at all “natural” for anyone.