I'm going in August, and I'm going to use the opening of Diagon Alley to explore and enjoy Hogsmeade a bit more. Crowds should be less there than usual with everyone flocking to Diagon. But that's just me. I went the week between Christmas and New Years in 2010 and it was absolutely insane. They actually had to shut the doors of the parks around 2:00 for three straight days, which wasn't happening with any Universal parks at the time. I just don't see Diagon being quite that crazy.