When we did it, we were near the front of the line for sign-up, and we did the very first show because the day we did it, the first show was 10-15 minutes after park opening. So, instead of having to arrive 30 minutes prior to a later showtime (resulting in a total experience time of 45-50 minutes), we were finished by 9:45 or so. We had fast passes for Toy Story and Tower of Terror, and Star Wars, so missing that initial rope drop time didn't hurt at all (kids are too small for RnRC). Plus, you're already missing the first bit of rope drop touring due to having to sign up for Jedi in the first place (by the time you've finished, at least some lines will have started forming at the headliners).
On the flip side, doing later in the day when lines everywhere else are long is a good plan too. And showtimes don't always start as close to park opening as ours did.
Even in the 9-10 AM hour, it was still super hot when we did it (this was early Sept. 2015).