I have a 4 year old and a 2 year old too.
During the week, they're asleep by 8:30 ish. Sometimes a bit earlier, sometimes a bit later.
They get up beteeen 6:30-7 am ( today at 6 ).
They can totally handle being up later sometimes and also being out and about.
When we go on holiday in the summer, they have a late nap and stay out until 11 pm, no problem. We tend to go to Italy, where that is completely normal in the summer. But they do have a big nap in the day to facilitate that and they get up late as well.
We recently had a big birthday where we celebrated until 11 pm and they were ok. We don't do it often, but they're totally ok if it happens.
We've done stuff like that since they were tiny babies, maybe that's why. Also in laws often used to come over at the weekend after work 8:30, so the kids would be up until 9:30-10 at weekends regularly so they could see their grandparents.
They don't come over at that time much anymore because it was annoying to be fair. But the kids never showed they were over tired or anything like that.
It depends on the child, as always. They're all different.