> Do you think our ancestors slept exactly 8 hours a night from 10pm to 6am?

Yeah I pretty much do expect that (but more like 6 or 7). They were awake a few hours after sunset by fire light, then get up fairly early. I certainly don't imagine them napping during the day, when they could be working together to get food, unless it's a climate where it's too hot to do anything in the middle of the day.

Studies of modern hunter gatherers seem to back this up e.g. [1]

It's widely known that Victorians would have two sleeps over night, with a productive period in the middle, but this seems to be a misconception based on a passing remark in one court case. Even if true, this is a post-industrial society with unhealthily long working hours and I don't think we should be copying their sleep patterns.

[1] https://www.sciencedirect.com/science/article/pii/S096098221...