They do NOT allow you to overnight in the overflow lot... Arriving early (but not at 1 AM), might or might not work, if your site is ready they will likely let you have it. If it is not ready, I believe they will let you into the overflow and call/txt you when it is ready. I've read on other forums that folks will leave their rig in the overflow and go get some park time in while they wait for their site. If you've never visited, check out fortfiends.net. it's a great resource for researching all things Fort Wilderness.