After doing this last week I will tell you don't stress out about it. I was stressed that we wouldn't make it into a time slot, and everything worked out perfectly.
There are I believe 12 kids in each training session. Someone posted the time slots and I counted 15 of them. That is 180 kids, give or take if they change up the number of shows, etc. So as long as you are there at rope drop and head right to the sign-ups, you should be fine. If it's raining, they will cancel, so just be mindful of that. It was drizzling when we came out of Hollywood and Vine, and the first 9:20 training did get cancelled. We luckily were in the 10:10 training, so we were the first of the day. Here is a play by play of our experience. We had a 8:00 Hollywood and Vine ADR. We got right in, the characters came to our table right away, and we were done with everything by about 8:40. We saw it was raining outside, and hung out for a few minutes, as I didn't see people passing by, so I wasn't worried that the park was opened yet. We went outside about 8:50, and I realized the park had opened already, so we walked over to the sign-ups (which was about a 2 minute walk, if that). I was a little worried, because I wasn't sure how many had already signed up, but we got in line, and waited for a few minutes before it was our turn. When we got up there they asked my nephew his first name and last initial (to put on the little slip they give you as your "ticket" to come back to the training) and asked how old he was. He told them 6, then she just said something along the lines of "are you ready for Jedi Training" and he said Yes. She asked if the 10:10 show was ok, and I said yes. She printed out the slip and told us to be back at 9:40. It was around 9:10 then, so we didn't want to go far. It was still sprinkling, so we just hung out around the building and then got in line. They lined us up at the Sounds Dangerous building, and then to kill a little time the guy started asking some Star Wars questions. Some of the kids were answering, some weren't. Not a big deal, just something to kill the time. They then handed out robes and lead us over to the stage. Once at the stage the Jedi Master came out and all of the kids took their spots. They gave them instruction on how to use the light sabers, how to do their battle, then practiced it a few times. Then the door opened and Darth Vader and the Storm Troopers came out. Each kid took a turn and if any of the kids were having trouble the Jedi Master helped them out. After they all battled, Darth Vader left, then they did the little bit with the Storm Troopers not being able to leave. Once they left, the kids all were told they did a good job then received their diplomas. The photographer took pictures of all of the kids throughout the Training, and gave each adult the photopass cards. The cards have all of the kids in training on it, and if you take it to "Cover Story" at the front of the park they will go through them with you and put just your childs pictures on your Magic Band/Memory Maker. Any questions you might have please let me know.