I was just in WDW from 5/5-5/10, before I left I checked the weather and it called for rain every day. While I was there, it was beautiful during the day and rained in the evening, usually around 7:00 or so, it rained for a a few hours and then stopped and it was nice again. The only day it actually rained in the afternoon was Wednesday and it was a down pour for about an hour around 1:00 or so. It cleared up nicely for a few hours and then around 7:00 rained again.
It really was not bad, I was able to get done alot during the day, in the evening I shopped or went back to the hotel to rest, one night I went to the movies. The parks were open pretty late so once it stopped raining, I went back to a park.