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Oh, there’s tons of evidence for this, largely in the writings of pre-electricity figures who clearly treated the subject as common knowledge. Advice manuals from the time even indicate that this was the best time for couples to conceive.

Modern tribes without access to continuous light actually still sleep like this too, which is fascinating.

https://www.bbc.com/news/magazine-16964783

Anecdotally I remember reading that in Britain it used to be more common for some to wake up in the middle of the night and do light reading, but you’ll probably want to do some more research as I don’t recall the source.

Maybe check the references in this article?

https://theconversation.com/did-we-used-to-have-two-sleeps-r...

Biphasic sleep is pretty common in Asian cultures. An afternoon nap is common in pre-schools and elementary schools, less common but still not non-existent in higher education and the workplace.

Compare also https://en.wikipedia.org/wiki/Siesta