As mentioned, you will only be allowed to check in once the system resets for the new day.
There is no guarantee that the room will be ready and you may have to wait but there will be no charge and you can get your keys, dining plan credits (if you are getting a dining plan) and your tickets so you can head to the parks.
However, if you really want to be able to check in and have the room, then yes, you would have to have a check in date of the day before and let the resort know you are going to be arriving very early in the AM the next day.