You probably already new this, but it seems humans generally sleep in two shifts in preindustrial times https://youtu.be/st_Ah6Ykbh4?si=dVZjsE9TvmZhQlnL. Just a neat thing you could probably use for world building, maybe in your original work as it's pretty hard to put in a fanfic, as those worlds weren't made by the original creator with it in mind, and a lot of them have artificial light anyways.
Of course, it was instantly accepted by everyone with no one contending it.

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