Definatly give yourself two hours from park to boarding the ship. The traffic is usually not bad on rt 520 which is the road your will be on the longest, but it can take you awhile to get back to your car from the park, and the rental company will also take a little time. Bear in mind the parks are jammed that time of year. It seems that you will only have about 4 hours total at the park and the lines can be 90 minutes long for each ride or more. Another thought would be Kennedy Space center which is closer and awesome.