You can check in as soon as you arrive at the resort, but rooms are not supposed to be ready until after 4 PM. That being said, we have occationally gotten in early in the day, but usually we are given a call back number that we call off and on until our room number is posted. No need to go back to the check in though, because you will get your keys as soon as you check in, but they will not be activated until your room is ready.
Why only 2 nights?