There is no specific check in/check out times. It's all first come/first served. Just pull in and park in an available spot. When the shop is open, let them know and maybe make a purchase. Not sure about the rules across the street where you pay for your spot and have electric hookups.

There's really no place to check in. When we were there it was just an open parking lot.

I don't know when the gift shop opens but the gate into the park opens at 8 am.