As to what's too early, I think that depends. Where I camp, most people are packed up and out by about 10 am. Rarely is someone still there by noon unless they are staying another night. Usually, they have breakfast, take a nice hike or such, then pack up and head out.
And most of the campgrounds have a 2 hour gap between check in and check out. That's so they don't get road congestion inside the campground as people are trying to get in and out at the same time. It also gives the camphost time to do a campground run to post reservation cards, clean bathrooms, etc., before people are moving in.
Fortunately, in the off season, they rarely have a problem if you want to stay later than the scheduled check out time unless someone is reserved to move in or it's a Thursday, Friday or Saturday.