I asked the same question and was told "it depends".
I thought that was a stupid answer, but it's right. Crowds vary a lot.
We went Monday, and I had to go to the 10:15 show due to a conflict in dinner obligations with local family. I got FP at about 1:00 or so, and they were Yellow for the 9:00 show. I spoke to a CM and they switched them out with me right there for the 10:15 show.
For the 10:15 show, they didn't even sell out. Blue was gone, but yellow wasn't that busy, and they let anyone in closer to showtime, even if they didn't have a FP. We had one, though, so we got in earlier, and had rail spots front, wet, and center.