There is a long discussion at the touringplans.com website in the Crowd Calendar section about Saturdays not being higher than 4th most crowded day of the week at any WDW park. They back it up with data from the transportation department, AAA and hotel bookings. The short explanation is that Saturday is a travel day. I'm going to test that theory by taking note of the actual wait times vs the UG predicted wait times for Saturday, Oct. 18 at MK and I'll post the results when I get back. Here is a quote from their website: (Note that this is from the publicly available section, not the subscribers only section)
A couple of interesting things to note in the above graph: First, 25 to 50% more guests visit the Magic Kingdom on Thursday than Tuesday. And more guests visit any Disney theme park on Sunday than on Saturday. In fact, Saturday ranks no higher than fourth (Epcot) on the list of busiest days at each park, and Sunday was listed more frequently than Saturday for every Walt Disney World theme park.
They predict a crowd level of 4 for the day of my visit (again, this is from the non-subscribers section) which means peak waits of 35 - 44 minutes. Unless they add the 18th as another FF day for HHN we will test the accuracy of these numbers. They predict the 17th to be a crowd level of 6 and, since we could go on either day, we are hoping their predictions are accurate. But we'll let you know.