"westernrvparkowner" always gives a good perspective. I think everyone has experienced getting to their campground a little early due to unusually light traffic or a short drive day, but I don't think you can automatically expect the campground to let you in early. On the few occasions we were ahead of schedule, we try and call to see if there will be an issue arriving early.
Some always ruin it for others. You let them come in early and then they stay late and pretty soon they start doing it on a regular basis because they get away with it.