We arrived to the HRH at 8am, got our magic keys, and went to the parks. The only thing is, your room may not be ready until 4-5pm. Most people check out late, or self extend their stay, so rooms are ready late in the day. You could come back to the HRH and go to the pool. In our case, we walked the garden path surrounding the hotel taking pictures.
The next morning you can visit the parks for a couple hours, check out of your room, then go back to the parks one more time.
It can work, but your trip will seem like it's over real fast if you only stay one night. Two nights will be much better if you can afford it.