Hi:
Some general thoughts on May --
1.
Weather. Absolutely stunning. There should be low humidity, temperatures in the mid-70s and lows in the mid-50s. Truly a gorgeous time of year to visit.
2.
Hours. You shouldn't have any issues at all with shorter hours. Hours should be normal, if not expanded, based on crowd anticipation.
3.
Crowds. Generally speaking, crowds should tend to get heavier as the month goes on, with the weekends being generally crowded regardless.
Disneyland and California Adventure are truly "locals" parks, and as such, the weekends are just generally crowded. This additionally becomes true as kids are let out for school in the summer (summer school closures tends to begin around late May and run through mid-June).
4.
Memorial Day. You can guarantee that the parks will be very crowded over Memorial Day weekend, which is May 22nd (Friday) through May 25th (Memorial Day/Monday).
All in all, I would shoot for early-mid May and try to incorporate as many weekdays as you can, to avoid larger crowds. Generally speaking though, May is a great time to visit
