For a 9am opening, arriving by about 8:15 should hopefully put you near the front of the crowd. If opening is at 8, and you arrive between 7:15-7:30, all the better as many people will not get up that early. Head straight to sign ups - many people will literally run, but if you don't need a very specific time or require being in the first couple of shows, I don't think it's necessary. You *may* still be able to walk and get one of the first couple of shows, but I'd only say with confidence you could count on it if you ran.
When I did this and walked briskly without running, we were the first people where the line began extending outside the building & the zig-zag inside was full. It took us about 20 min (despite posted opening time of 9, they let us in around 8:45 and we were finished by about 9:10). All 3 of the first morning shows were full by the time I got to the front, which was fine with me as I wanted afternoon anyway. They do let you choose from any available time slot and can help you rearrange FPs if necessary to accommodate.
Don't forget that all kids who want to participate must go to sign ups with you. When choosing a show time, you will need to check in 30 min prior to the show and the show lasts about 20 min.
Another strategy is to try to book a pre-opening breakfast so ou're ahead of the crowds for sign ups - I have no knowledge of that, but a search of these boards should bring up several threads about it. Good luck!
I am taking 3 Star Wars nerdlings (ok really 5 counting my DD and myself) to WDW world the first week in August. Yeah hot, but this was the only time SIL could go, then he backed out last week. 
Anyway, there are no EMH for HS during our stay. If we head straight for the Jedi sign up line at RD should we get in and how long should we expect to wait?
