Beckles is right. You must first check in to the hotel. Your room key card is your FOTL pass. You must show it at every attraction to get to the "Front of the Line".
We, too, only stayed one night (at HRH). We arrived about 1 p.m. and found that we were able to do everything we wanted by about 6 that evening at IOA. We rode many attractions twice. Be aware, though, that at certain times, they will only allow you to ride an attraction once during a two hour period. We had this experience at Spiderman. Early in the day we rode it over and over again...no problem. As the park got more crowded, we could only ride once during a two hour period.
FOTL is awesome! Have a great trip.