South of the Boarder camping reservation?

Hi, I'm thinking of using the campground at SoB on the way down to FL - and I'm wondering if I should make reservation. I'm visiting during the midweek at the end of June. I prefer not to, in case I can't get as far. SoB is my goal.

Also, I will be arriving late, probably - will there be problem arriving around 9 p.m.?