We very often find our visits coinciding with GayDays, as that is the week after school ends and before summer daycamp starts.
IME, crowd levels on Gay Day at the MK tend to vary greatly by time of day, and by what is going on that night and the previous night.
Your best bet is to go look at the events schedule on the official GayDays website. If there is a major park party the night before, morning crowds will be lower, and if there is a major park party late that evening, the crowds will be lower after 4 pm. However, if the parties don't coincide, you can expect the park to be crowded for much of the day.
One thing that I have noticed over the years, however, is that as the event becomes more well-publicized outside of the gay community, a lot of straight tourists will make it a point to avoid the park of the day, which ironically can cut down on the crowd. We went one day where MK was the designated park, but there was a HUGE ticketed evening party at DHS. A lot of attendees chose to leave MK in the middle of the afternoon and not come back, as they were headed for that party. The park was amazingly empty after 6 pm, because of all of the other tourists who had deliberately avoided it that day.
Speaking of which, if you don't hop, and you want to get your money's worth with long park hours, do check on those private in-park parties. When they happen, that park will close early, even in high season.
