The booking window states when campsites will be available to reserve. It is expressed as the number of days prior to your arrival date that you may book at a location.
Different camping types have different rolling booking windows:
A rolling booking window allows you to book a reservation within a specified range. The date that can be reserved will update each day at 9 a.m.
There is no guarantee that your desired reservation dates will be available once the booking window opens due to a few possible reasons:
Arriving on your scheduled arrival date but after the registration booth is closed
Arriving after 2:00 pm of the day following your scheduled arrival date