As others have said, take a day or two, or possibly three, to do off property things. Do half days to allow either the rest of the day to relax, or to coincide with off property activities. For example, go to GatorLand during the day, then later that evening, either go into a park, or have supper at a resort. Our last trip was supposed to be for 10 days, but we ended up skipping the last day and going home early because I wasn't feeling well. We are going for 11 days in April (10 days at Disney and one at Nickelodean Suites). Just to give you an idea of sample itineraries, I will post my itinerary from last time, as well as my itinerary for this coming April.
April 2011
Monday: Arrive at Wilderness Lodge in the morning. Went to Downtown Disney. That evening, we went to Kissimmee to do our Walmarting and played mini-golf at Pirates Island, where we play every year.
Tuesday: Universal Studios. Finished up fairly early in the afternoon, then went to the Beach Club for ice cream at Beaches and Cream. We enjoyed the resort the rest of the afternoon/evening, with supper at Whispering Canyon.
Wednesday: Islands of Adventure. Got back around 4 PM or so, did some pool time, and then Hoop Dee Doo, followed by a wagon ride, which parked at the lake to watch Wishes.
Thursday: Magic Kingdom all day and evening, with a midday nap/pool break in the middle. Supper at Crystal Palace.
Friday: 8 AM breakfast at HollyWood & Vine, and DHS until midday. Back to hotel for nap/pool break, then the rest of the evening at Epcot, including supper at Via Napoli and EMH.
Saturday: GatorLand, followed by the Florida Mall. Back to hotel for a while, then supper at Chef Mickey's at the Contemporary.
Sunday: Initially planned to go to the ocean for a couple hours. But my wife has a cousin in Orlando that she wanted to meet up with, so we took the boat to Ft Wilderness and hooked up with him and his son there for a while, and had lunch at Trails End. For supper, we went to 1900 Park Fare. We did some pool time at the resort that day, and my son and I did some monorail riding.
Monday: Animal Kingdom unti early afternoon. Then back to hotel for pool/nap break. Then DHS in the evening, with supper at Sci-Fi.
Tuesday: Epcot AM EMH, then Epcot all day and evening, with midday break in between. Supper at Garden Grill.
Wednesday: This is the day that we were supposed to have had breakfast at the Crystal Palace, then spent the rest of the day and evening at the Magic Kingdom, but we ended up leaving to go home instead.