We saw them a few weeks ago, and right at MGM opening (at 9 that day) they came out right by Sounds Dangerous. We were one of the only guests going that way (away from ToT and toward Star Tours) and had them to ourselves for about 10 minutes. I don't know how often they're there, but something to consider. This was from about 9-9:20 am.
They also sold CARS stuff in the stores in MGM, and I saw CARS balloons everywhere.