Not only do the days of EMH sometimes change from month to month, but on occasion, as on my trip, the EMH days change even AFTER they have been posted online (something they claim they will never do).
This became a real issue for me because I had planned all my PS's as soon as the dates were available online. I came up with a schedule based on which park I'd be in and what time I needed to be at the gates. When I finally learned the EMH days had switched (only 2 weeks before my trip), I had a hard time getting good PS times.
All worked out in the end, but I had to cancel and reschedule alot of meals to be able to get to enjoy the places we wanted to eat.