When I made reservations for this trip in May, I checked the Conneaut Lake website to make sure they would be open on a weekday on the first week of September. The website claimed they would be (specifically, the web site said the park would be open weekdays until Labor Day).
I then called to make a reservation at the attached hotel and specfically asked about the park being open. They placed me on hold, then came back and told me the park would be open. I made the reservation.
Unfortunately, when we arrived, on the day of our reservation, the park was closed. They gave us our reservation deposit back, which was cool, but it was still kind of a bummer. If I had known it would have been closed weekdays that week, I may have tried to reschedule to get their on a weekend.
I will probably incorporate this park into one of my annual Cedar Point trips in the coming years.