For me, it really depends on how quickly you want to turn around once you get to the resort. With a 1:15 pm flight arrival, you will probably get to the resort around 2:45/3:00 pm (depending on how they load the buses, traffic and how many resort stops you make). That means, your room may very well be ready when you arrive. Do you want to go to your room and freshen up? Do you just want to drop any carry-ons at bell services and beeline to the park buses? If you plan on spending the rest of your evening in a park (both will be crowded), I would probably make the first FP+ for around 5 pm. This gives you some wiggle room at the resort, to get through security at the park and to make your way leisurely to your first ride.