You can check in as soon as you arrive, and they will give you the card that will be your room key and your UPH. When they assign a room to you later in the day, they will activate the card for the room then. At least, this is what happened to us. There is a chance that you will still have to go back to the check in desk and switch cards later, if they don't 'activate' properly (this also happened to us).
It is possible that you will be able to check into a room right away (has happened to us several times with early check in) but don't count on it. They will store your luggage for you when you check in though.
I may be wrong, but I don't think there's any way to get your UPH's without checking in.
