In the lower 48, it seems that the check-out time is 11:00 AM at most places that we have stayed and some offering 12:00 noon.
At the Meteor Crater RV park near Winslow, AZ, has a 1:00 PM check-out so that the RV'ers can go down the road to see the 'Meteor Crater' that happened 50,000 yrs. ago. Otherwise, I've never seen super early check-outs. We don't stay at public campgrounds so that is probably the reason. :D
We would probably pay for an extra day if it was anything earlier than 11:00 AM. I get up early, but I enjoy my mornings drinking my coffee, watching the news and reading on my laptop. Being retired, the world moves at my pace. :p
Safe travels,
MM.