I did thay once and my spot was reserved. There wasn't any other spots available so we ended up going somewhere else for the night.
Summer time the spots are rarely open a day early, but the day of your reservation it is often possible to get in beforehand. Just show up, and if your site isn't ready, you may have to spend some time walking a beautiful beach.
If they have your spot. If not you can stay in another for the night.
You'd have to call and see if any one else reserved your spot. We were able to check in very early because the people who rented our spot left early.
Thanks! Your answer is awaiting moderation.