We showed up at 1 thinking it was the check-in time and even though our site was vacant they would not let us in.

As I recall from my stay last year, it depends on when the site frees up, but I believe they stuck with the usual afternoon check-in time for new arrivals. Questions like this are best directed to the campground to see what is going on there before you arrive.

They are very strict about letting people check in early; as in, they won’t do it. But the visitor center is very close to the campground and there’s plenty of parking there.