trying to do both Pisa and Florence in one day is tuff. U can do it if you hire a private tourguide. They will maximize your time in both Pisa and Florence; and get you back to the ship in plenty of time. I used Romeinlimo for my stop in Florence/Pisa; they met my group at the port with two nice size air conditioned minivans. the driver/guides were great. They know the area; know how to get around the area; and will give u some great facts about both Pisa and Florence. One thing I liked about www.romeinlimo.com
they can pull their minivans right up next to the tower of Pisa; where tour buses have to park several blocks away. A great way to see both cities and still make it back to the ship.