It really depends on the county and sometimes the individual district. My cousin lives down in South Florida and I know her kids are out before Memorial Day. Actually it's usually closer to Mid May. Also, keep in mind that Florida Residents are elgible for a discounted resident pass that is only able to be used until June 7th of this year before blackout dates begin. I'd guess that a lot of Florida schools are out before then. I know my cousin plans on going up as soon as her kids are out of school to take advantage of the cheap pass. She says a lot of Florida residents do this!!! Also, there smart enough to avoid WDW during the summer heat, unlike me!!!
Actually there are 2 Florida passes - the Seasonal pass and the Annual pass. The Seasonal pass is only good for 4 quieter months (May, September and 2 other months that escape me at the present time). The Annual pass is good all 365 days. We'll be some of the crazy Floridians joining you in the summer with our annual pass!!
Actually, the Florida seasonal pass is good for more than 4 months. The black-out dates vary from year to year but are generally the summer months and major holidays.
Here are the black-out dates for this year. You can use the pass on any other days.
December 21, 2002 - January 4, 2003
April 12, 2003 - April 24, 2003
June 7, 2003 - August 14, 2003
December 20, 2003 - January 3, 2004
Hillsborough Cty Schools (Tampa) get out at noon on Thurs, 5/29. It's kinda crazy. We get Monday off for Memorial Day and then go back for 2.5 days. Doesn't seem logical, but then nobody asked me, ha!