...but with a bit of thought, and a reservation in a Disney hotel, it is open for 16 hours a day - and there will be bits that you don't particularly want to see....like the Country Bear Jamboree, Cinderellabration or Sleeping Beauty (I'm guessing).
You HAVE to see the fireworks in the Magic Kingdom and in Epcot (it's Florida law, or at least, should be).
Mandatory Rides: Epcot - Mission:Space and Test Track and Soarin (the latter of which isn't yet open - will be in two weeks). Magic Kingdom - Space Mountain, Splash Mountain and Big Thunder Mountain. MGM Studios - Rockin RollerCoaster and Tower of Terror (should also catch Indiana Jones show).
Have to say - the parks can be a bit pricey - there are deals to be had (try
www.mousesavers.com for tickets).
Send me a P.M. with your questions.
Having said all that - I trust you will be arriving in Florida having already passed all your PPL written exams and the R/T test!!
Three weeks at that time of year is not an easy call. You fly into Orlando or Miami?