We did it once Wed evening......actually DH rode it first with wait time of 10 min. then we all did it with a wait time of 35 min. in the stand-by line.
The park was unbelievably crowded!!! And I think a lot of people are still not sure of what to expect, so it wasn't nearly as crowded as TT.
Comparing the 2.....we liked TT much better.
M:S was cool, but not something we would consider riding over and over.
We then went back and did it twice on Thurs. We got right on at park opening.....wait of 5 min. But by 10:30am...wait was up to 60 min. We were heading out at 11am, but another guest gave us their FP, they already rode once and did not want to ride again.
We did not notice any difference in the seat positions. You can switch around with the other guests if they want to.
If you get a FP, check the time it states you can get another. It is usually about one hour after you got the first one. Or close to the "ride" time of the first. Then before you get on using the first one, get another one. That will save few minutes.