I noticed that the close time is 4pm does that mean I can't come in too camp for the night after 4?

Of course you can. The gate is always open. Just do like I did: When you at the gates, check which locations are free (there's a map with free and already occupied locations), then get in, find which free location you like, go back to the gate, pay by placing the money in the envelope you can find there and place it in the box, mark on the map your location, place the ticket on the rear view mirror and enjoy.

Yes