We just returned from our FOS cruise (loved it!) and did something similar. We flew into Orlando Saturday but arrived really late so stayed at a hotel near the airport (Holiday Inn Express and Suites) then took a pre-arranged shuttle (Cortrans) from the hotel to the port. Then after the cruise we rented a car and spent the day at Kennedy Space Center. We stayed that night at a Disney resort (we used DVC points), and swam, had a nice dinner, watched the fireworks. We didn't fly home on Mon until 7pm, so we took the monorail to the Poly for breakfast, visited a few resorts, had lunch in Celebration, played mini golf at Fantasia Gardens, got ice cream at the Dolphin, then returned the car to the airport. We rented through Budget and it was $127. We saved multiple hundred dollars flying home Mon instead of Sun, so that's the only way I could convince DH to let us get our Disney "fix." There's plenty to do at Disney if you do arrive on Saturday.