We had the two day pass due to my two small children. Didn't seem to be that many people especially in the middle of the week.
You never can predict the wait
It is always pretty busy, so I'm not sure EXACTLY how busy it is in May. However, the fast pass depends on how long you are willingly to wait, AND pay, because there are different "levels". If you don't want to wait, you CAN buy it, but it's pretty expensive.
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