Some CGs have an overflow area that you can temporarily park in. I think, and may be wrong, that most CGs will want to charge you full rate even if you are just doing a short in/out layover. It's been our experience so far that CGs are pretty easy-going about staying a bit late or arriving early. The exception to this might be in the peak season or on a holiday weekend when CGs are very busy. Sometimes there can be a lineup waiting for a site to become available and it's not fair to make them wait.
We only use private membership CGs. State and other similar types may be quite different. I think some of these even close their entrance gates in the evening and no one is there that can let you in.
Many CGs let you arrive early or late, but in fairness to others, I would wait until a more reasonable hour in the morning before you set up so you don't make noise that will disturb others. Same if you arrive really late, wait until morning before you fully set up. Electric jacks are pretty dang loud but manual jacks would be okay. If you pull into a site, try and shut your engine off at earliest convenience.
We've occasionally had someone with a diesel will pull in nearby early or late and leave the engine running while doing a full set up and they have to shout to hear each other over all they noise they make. Grrr... :(
