We are camping Friday and Saturday night I'm off Friday our campsite is available for thursday night so does that mean I can arrive early on Friday instead of having to wait till 3 to check in

I would call in the morning. I am pretty sure they do early check in, but you have to call.

As said above either call about 9 tonight or first thing in the morning if you don't want to reserve it tonight .

I'd call and ask. Always a chance a walk up could have it on Thursday night at last minute. Most are good about early check in if site is available. But not guaranteed in my experience.

You can take the chance or book it for Thursday night