What do you mean by FP wait times? The wait to use a FP that you already hold or the wait in line at a kiosk to get a FP.
Also, do you have specific dates in mind? As the PP said, May has things like Star Wars weekends at DHS and Memorial Day weekend, but some less busy times early in the month.
You might want to check the May crowd calendar on the easywdw site to get an idea of overall crowd levels and recommendations on which parks to visit which days.