Hi Karen!
Disney's Magical Express is a great way to get your trip started because it's such an easy and convenient mode of transportation from Orlando International Airport to Walt Disney World Resort. I always recommend allowing three hours between the time your flight lands and when you will be at your Disney Resort hotel ready to start your first activity. This allows time to get through the airport, get boarded onto Disney's Magical Express, travel to Walt Disney World Resort and make stops at other Disney Resort hotels before arriving at your vacation "home".
Once you arrive at Disney's Port Orleans Resort - Riverside or Disney's Port Orleans Resort - French Quarter, if your room is ready, you can make a trip to your room to drop off any carry-on items that you don't wish to bring with you to the theme park or you can check them at Bell Services before heading to your dining reservation!
50's Prime Time Café is located in Disney's Hollywood Studios. While you didn't specify whether you were staying at Disney's Port Orleans Resort - Riverside or Disney's Port Orleans Resort - French Quarter, both will require a bus to get to Disney's Hollywood Studios. So simply board a
complimentary resort transportation bus from your hotel to Disney's Hollywood Studios to enjoy your meal. I recommend allowing one hour transportation time, so given your flight arrival time and your reservation time, you should have plenty of time to get to your early dinner!
Please let us know if you have any other questions. T-T-F-N, ta ta for now!
~Crystal