I found this on the Theme Park page:
Kids must line up before the show(s) and will be put on a list.
The first show's list will be filled, followed by the second show's list, third show's list, etc.
All of the show's quotas will be filled, in order, and once filled (unless someone drops out, which IS very possible)
no more names will be taken.
So, yes, it IS possible that all of the show's positions can be filled by mid-morning, or so.
I'd arrive early and head directly to the Jedi Training area.
Hope that helps.
Sal