They told me they are gated at 6. Does that mean we have to be in for the night at 6 or can we come and go after being checked in?

Yes, you get a pass card.

You will have to check in before 6 PM .no one will be in the office after 6pm . They lock the gate coming in at 10 PM . Until 7 AM. Then you can come and go as you want . They will give you a key at check in. If you are out after 10 PM you will have to park outside the gate and walk in .

Once checked in you are given a gate card that allows the gate to be opened after 6. But all vehicles have to be in the gate by 10 pm or you will have to park by the office and walk in.