I think it was 6 days. Summer 2008, we had planned to take our then 6 and 8yo sons to COSI (great science museum in Columbus, OH) and then spend a couple of days at nearby Kings Island. DW reminded me that we had 3 days left on no expiration tickets to WDW, and asked if we might find a deal on a hotel near the world. Found that the Radisson LBV had just finished a renovation and was offering rooms for under $100/night. Since the tickets were already covered, we realized the difference in gas for a 200 vs. 2000 mile round trip was about the only difference.
Best part--we didn't tell the boys we were going to Florida instead. We got up at our usual 2:00a (usual for a drive to Orlando, not to Columbus) and piled the very sleepy kids in the van. About 30 miles from home, older son said, "Why are we driving south?" and then hit us with the most surprising words I think he's ever said:
"Are we going to Disney?" (Long pause.) "Oh, man...I really wanted to go to COSI!"
This boy loves WDW, but he really likes science, too. I had to spend a few minutes reminding him that EPCOT has a lot of science exhibits, and that they are just as hands-on as any science museum's. As you'd imagine, we all had a great time, but it was a litte dicey for a few early morning moments!
Last minute trips are awesome.