I think it will depend on how much rain they get. If its just a light sprinkle they most likely will stay open. Its still Spring Break season. And unless the park becomes a ghost town where it doesn't make sense to stay open, I'm thinking they will remain open as close to the normal times as they can. I know a lot of people vanish from the park when it rains, but if there are enough that are only here for break who can't just come back later stay in the park... might be busy enough.
It won't close early. Especially because its spring break. When the park closed at 6 a few nights earlier this year, it was during mid-week of the off season, there was literally only about 2000 guest in the park. Everything was a walk-on. It was smart (but insanely rude) to close the parks early then. Now during mid-spring break. There is no reason to.