It looks like both parks will be open from 9am-8pm all the days you will be here.
As for crowds...since it's at the end of the week, you won't be getting a lot of a locals crowd. Schools in the area either have already started or go back next week so they will be in school. You will get the end of the year tourist crowd, but I really don't expect it too be that terrible. You might want to look into getting Express passes though. I just think they are a GREAT idea so you can get in as much as possible.
As for the rain...it will. There is no denying it. We get rainstorms almost every afternoon but they don't normally start until about 3pm or so. My suggestion would be to go early, get in as much as possible, then do some of the indoor rides and shopping in CityWalk during the storms...hopefully you will get lucky and have nothing but sun, but don't count on it!