They hours were posted correctly...at the time they posted them. Then they made decision to change the hours, to add more time to the park, not take away anything from anyone who had previously booked tickets for that park, which you hadn't even done.
Just like when someone buys something for full price in June, but then that particular item goes on sale in August. In June, the posted price was correct. The store then decided to put that item on sale, and changed the price, not because it was incorrect in June, but because they made the decision to change the price.