It doesn't matter what time it is go to the front desk and register. Most likely your room is not ready yet but if it is bonus points for you! Go to your room and get comfy!
If your room is not ready (and most likely it won't be) the hotel should be able to store your luggage for you. Some places you give it to the front desk person and others have a seperate bell service or storage area where you drop it off. They should tell you when you drop it off if you have to come back and pick it if or if it will be delieverd to your room once your room is ready.
Once you have gotton rid of all your extra luggage etc. If you don't want to burn a day on your pass then
Go have non park fun! check out all the cool things at the resort, go for a swim in the pool, go to another resort for lunch, go play put put, or go to downtown disney for plenty of things to do food, shopping, a movies, or even disney quest (video games).
Depending on how much traveling you had to do and how tired you (and the kids?) are, going ahead and going to a park may not be a bad idea. Extra park day are not that much more expensive on the longer tickets, and if you head to say epcot that is always open till at least 9pm you are still getting plent of "time" for your days ticket. ]
No matter what HAVE FUN!