We booked a tent campsite 5 days in advance. When we stayed the first time with my parents they had booked 4 nights and then we just kept calling to extend the time. I will say that the time we booked 5 days before we had the LAST campsite.
oops miss read. I would think that you can book within the booking year…at least on the web. I remember looking in February at the November and December slots and would have been able to book then.