Hi Shannon!
Welcome back to the Disney Parks Moms Panel. Wow, it sounds like you are in for a magical trip with the
Disney Fall Feast 5K and a
Disney Cruise all together! I actually reached out to some of my fellow Moms Panelists to see who had experience with this and several of them did.
Make your
Magical Express reservation with your arrival flight information, but tell them you will be returning to rent a car and don't have a flight out and they'll leave the return trip blank. When you board the Magical Express, as you are leaving Orlando International Airport, the Cast Member will likely confirm that your return trip is blank and you can let them know you're aware and it's fine!
Upon check in, arrange with the Concierge or Front Desk for your return trip. You will receive your Magical Express paper on the door as usual, but it will give you instructions to call a specific number. They will reserve a seat for you on a properly timed bus and provide you a voucher number. A Cast Member at the Front Desk will use this voucher number to provide you with the documents you need to board and head to the airport. This gives you some flexibility to decide what time you'd like to return!
After you return and pick up your rental carl, you'll soon be on your way to enjoy the high seas with Mickey! I hope you have a magical trip and please let us know if we can help in any other way.
-Lindsey