When we do TSMM first thing after RD we take the same route as the rest of the crowd (assuming we do RD on Buena Vista St). 95% of the crowd turns left into Cars Land and we just take the direct route towards Paradise Pier : taking the main walkway between Grizzly Peak & Pacific Wharf, turning left towards Ariel's Grotto, following the boardwalk past Screamin' & King Triton's Carousel and then reaching TSMM. The past couple of trips when we did TSMM first we were able to walk on and do it twice (the other week they let us stay on multiple times without getting off, but it was raining so that's probably why). It's been years since we've done RD from the GCH entrance, so I'm not sure if that's faster than the route from the "main" RD at Buena Vista St. But since Cars Land opened, anytime we've done TSMM first, we've found it to be empty first thing.