May is still within the off-peak season, so it is likely that there will be shorter hours during the weekdays. From last year's calendar, though, it looks like there were extended hours during the weekends.
Do you know if there's something special going on that week in May? Hotel rooms seem to be booked or more pricey for those particular weekdays. I thought it would be more of an off-season time with more room availability and good rates.
This may not be 100% valid - but as my Mom has gone to several dental conventions over the years, I don't think it will impact park crowds much. Maybe a little, but most of the people who attend don't bring family. Dentists themselves usually pay for their employees to attend.
And, right now, the dental field isn't doing so well. My Mom has been unemployed for quite some time (offices are laying off assistants), so I'm guessing even if some brought their families - they might not be able to afford visits to the park.