Not sure if you have already gone (this is an older post!), but from our signature it looks like you are doing a split stay. You would be eligible for it on the day you move from one resort to the next.
For my August stay I am not getting in until 10 pm. I'm going to stay off property that night, then drop my stuff at my WDW resort the next morning and head to the water park. I've never done a Disney water park so this perk is something my family and I are taking advantage of. If we don't like the park at least we only invested time and not money into it (although I doubt we'll dislike it!).