Hi Laurie,
The Walt Disney World Water Parks are so much fun. My family and I have very much enjoyed our times on the water slides and other attractions at
Disney's Typhoon Lagoon Water Park and
Disney's Blizzard Beach Water Park. I must admit that one of my absolute favorite things at Disney's Typhoon Lagoon Water Park is the stand that sells hot, freshly made mini donuts. It is located on the way into the park. Water slides and mini donuts are forever linked in my mind!
There are not discounts available for going to the water parks later in the day. However, you are correct that there is a currently a discount for Disney Vacation Club members visiting the Disney Water Parks. Currently, members can save $4 per person (ages 10 and older) and $3 per person (ages 3 - 9) at the Disney Water Parks.
I like to monitor mousesavers.com for current discounts available at Walt Disney World. To find current available discounts at the Disney Water Parks, from the mousesavers.com homepage click on "Walt Disney World" and then "Tours, DisneyQuest, Water Parks, and More" and then click on the link for "Water Parks."
I hope this information helps, Laurie! Have a great trip and please do not hesitate to ask if you have any further questions.