FW checks folks in 24/7 While the drive through check in is closed, they reception outpost desk is open.
Check in time is actually 1PM for campsites, not 7AM because check out is 11:00AM. You can't check in at 7am to get a site someone doesn't have to be out of until 11.
If you arrive prior to 1PM and you site is not ready, you can still get your resort IDs and enjoy the campground. There is a very large parking lot at the reception outpost, so you can stash the camper there and check out the pool or other activities. If you want, you can go to a park and make a day of it. When you return, get your site assignment and set up camp.
Now, with that said FW runs hot & cold on allowing folks to arrive in the wee hours of the morning and "sleep" in the overflow/day use lot. At times they have allowed it and at other times security asks folks to move on.
If you decide to stop just short of FW and crash in a parking lot, remember the closer you get to the Orlando area the more restrictive local governments have become on extended parking in lots. Depending on your direction of travel I would probably suggest stopping a couple of hours away and crash at a Cracker Barrel. They usually have RV/Bus spaces so you can stop, get a few hours sleep and when you get up have breakfast at CB. Then drive into FW figuring your arrival at around 8 or 9. At that time depending on your day pof arrival you may have a good chance of checking in and going right to your site. If not, at that point they will let you use the overflow lot, and as I said you can go to a park, enjoy the amenities of FW or cruise other resorts.