It's really easy to do. We've done it multiple times...through the DU offer.
If you do it through the DU offer, you should remember to bring your printed out info with you, to the bus. You will either make advance reserervations or you can just call Mears the day before to set up your time for pickup. The bus/van will pick you up in the bus area..usually around the DME bus stop area, at each resort.
The bus drops you off in the bus, taxi area at US/IoA. You just walk to the escalators and turn left, towards US/IoA entrance. Reverse it when you're ready to go home. Now...as far as time to go home...you can either reserve your pickup time for your return to POR when you book, or you can wait until mid-afternoon of your US/IoA day. You should then call Mears about 3 hrs prior to the time you want to leave and they will give you the time you need to report to the bus stop.