As suggested in an earlier post, we had breakfast at H&V last week (Fri April 15) so we could eat and line up for Jedi signup.
My DH noticed "the running of the bulls" while we were eating (so approx 8:30, 8:40am? -- park opening). I grabbed the kids and we lined up for Jedi signup, we were probably about 25-30 spots back in line (with some spots having multiple kids).
When we got to the actual signup tables, the next available shows were 11:10am (two spots left) and 11:40am. (I'm assuming shows later than 11:40 still had plenty of spots available, but that's an assumption so take it for what it's worth.) Both of those show times worked for us, so we were in great shape.
If you have more than one kid participating, try to have them in the same line/platform. My two got separated somehow, so DD7 was on the top platform fighting Vader and DS6 was on the lower platform fighting the Seventh Sister. The only hassle/snafu we had with that set up was we were only given one PhotoPass code to retrieve the pictures (DD7's). Once we got home, I called PhotoPass though and they were very helpful in giving me the lower platform code and I was able to claim DS6's pictures also.
Have lots of fun!!