Well, since Disney is the one setting the EMH parks/ hours, it is really the first place you should look. If anyone is posting hours that have NOT been released by Disney, then you should assume it's either a mistake or a guess.
With the current economy and park attendance fairly difficult to predict in advance, Disney has been getting later and later in posting hours. They've also been changing hours, sometimes even changing hours on the day you are visiting!
So yes, it's frustrating, and even if you see hours posted on the Disney site, they are not set in stone.