Is there a specific check in time? We are quite far and want to know what time to head out to allow for stops along the way.

No. It's simply an envelope system to pay for your site. But the sites are first come first dibs

No there is specific time to check in but it is first come first serve, I would make a trip when it is not a holiday. My boyfriend and I been there and it seems like it's not easy for anybody to find. Last time we were there it was not crowded.

Check in time is 2pm I believe. But all sites require a reservation, whether RV or tent site. You can set up reservations at travelok.com