Actually, after thinking about it some more and reviewing the pictures again and looking at the time stamps; I had the order wrong. It was the Ultra-marathoners, the Best Mates, and then the Momshells... with the Momshells lagging significantly behind the Ultra-marathoners.
We got to the park just before 8, just before it was opening (we actually got in earlier than normal visitors because we were part of an "internship" program) and the Ultra-Marathoners were already there. I overheard several people (park visitors) saying it was down to the final three, but judging by how tight-lipped all the crew was, this could have been just guesses on their part because we only saw three teams. It is entirely possible that others were there later than the Momshells (the picture I snapped of the woman carrying the two backpacks was as we were leaving that section of the park and headed to another)and we just didn't see them, but I am however doubtful that there was actually people there before the Ultra-marathoners. When we caught up with the crew, they were still plotting out where they wanted the teams to run and how they were going to get the next clue after they completed the challenge... so it seemed to me that they were on the first "run through" with the Ultra-marathoners. We actually stood around and watched the camera guys shooting b-roll stuff that they use for filler as they're explaining the challenges. That was kind of neat. It was also fun to watch the filming process as the whole thing happens a lot slower than what you see on TV. They had the girls sit down and read their clues, and then filmed them running around that area of the park. Then they'd set the cameras down and sit around and then pick them back up again to start filming again. So as a whole, the show is not nearly as spontaneous as it seems when you're watching it... but that's just part of the magic of television.
As for timeframes, as I mentioned the Ultra-marathoners were there when we got there and we stood around for probably 10 or 15 minutes watching them. During that time the guys showed up. We then went and did several hours worth of chores in the same cage area that the challenge was filmed and then broke around 11 or so for lunch and to go pet some of the pandas. It was on our way out of that area that we ran into the Momshells. We returned to that area around 1 or 1:30 to feed the pandas their afternoon snacks and by this time there was no one left with the flim crew. So if there were infact other teams still in the game, they would have had to have come through while we were gone as we were there in that cage area for the rest of the day. I guess they could have been EXTREMELY late though... who knows.
Since we were part of the internship program, we were allowed "behind the scenes" so to speak at the park... this is actually how we found the clue and were able to touch it. One of the teams had accidentally left it behind inside the cage complex where the pandas are. I will say this; the clue said that if they couldn't find a bus, they may have to find other forms of transportation to get them to their next destination... and that would be a bit tricky there as the breeding center is pretty well outside the main part of the city, and we didn't see any taxis or buses go by while we were near the road. It was busy there... but we never saw any public transportation. That should be entertaining to see how they get out of there.
No idea of if it was an elimination leg or not. As I said, everyone that we ran into was extremely tight-lipped with the exception of the girl who stopped us from taking pictures with the clue box. She was the one that told us the name of the show was China Rush and that it was infact part of the Amazing Race. My wife and I have watched only the last few seasons of the Amazing Race and had no idea they had it in China. The guide we were with had only read about it in magazines.
Anyways, I hope this helps. We were totally geeked about being there when they were filming it.
Dan