Million years? Absolutely no. Sleep schedule is something you can change, fix, break on demand with some effort and heavily depends on external factors.

For starters sleep cycle is not something hard-coded to the human system. Closer thing to that would be sleep ratio. For example 8(sleep) -16 (awake) is the most common but it's not even close to be the same for everyone. Many have 7-17 many 9-15. Many are unable to keep it in a 24h cycle, they will either sleep every day earlier or later and every now and then they will need to fix it (the latter is actually pretty common issue for many people nowadays.

Going back in the past as many people already mentioned is that humans before society required proper schedules were using biphasic or even triphasic sleep schedules. I still belive (personal experience) that biphasic sleep is superior however it's very problematic to follow in a modern society due to being often required to stay awake for 15+ h

Long story short like I said there are a ton of examples and each individual will adjust differently but I'm very confident that if for example we move to a planet with 36h cycle almost no one would keep their 8-16 cycle. It doesn't divide the day perfectly (and each day being the same) and it will be extremely wonky. I'm sure most would go to biphasic sleep cycle and do something like 6-12 and 6-12. Or maybe even triphasic 4-8 three times.

Some might try to have monophasic with naps or other crazy scenarios but doubt many would try to keep earths cycle