The first week in May is Pretty slow but they also do some kind of Physics week/math days, but the kids have activates that have to do and still leave pretty early. You can get a lot done early and later.
I went the Tuesday after Memorial day last year and was pretty slow and I think that week was kind of slow. A lot of the Ohio schools start Mid to late August so that helps in August. With that said a lot of Michigan school go back after labor day. Like said before the Week before the park closes for weekday operation is pretty slow. I have also been told the weekend before halloweekends starts is slow.
The thing is that with TT2 opening people might go early but that is still a small group of people.