Hi Stephanie.
Select attractions in the parks are open during Extra Magic Hours. At
Hollywood Studios, those attractions include Muppet Vision 3-D, Rock 'n' Roller Coaster, Star Tours, Toy Story Midway Mania! and The Twilight Zone Tower of Terror.
It's most likely that sign-ups for Jedi Training Academy won't begin until official, regular park opening hours and the opening of
Sounds Dangerous with Drew Carey since that is where sign-ups take place.
That being said, I would definitely say it's worthwhile to take a jaunt past Sounds Dangerous on your way back to Star Tours or Muppet Vision 3-D just to see if it is open, and if not, definitely plan to bee-line it there for 9:00 on the dot!
Star Wars: Jedi Training Academy is a very popular attraction that fills quickly for the day, and a definite "must-do."
Wishing you and your little Padawans a Magical time at Walt Disney World!
Kirsten