I can't tell you about May, but we just did June 1-5 at USO/IOA. I assume the crowds will be less in May than June. We stayed offsite at Vistana, so we went without the FOTL perk. We arrived at opening time and got most everything done with not too horrible waits. We went straight to MIB at USO and worked our way up towards the front and got most done by 1 pm. We did Terminator and it broke down. The afternoons got heavier with crowded; we left by 3 pm if I can remember. At IOA, we started at Incredible Hulk and worked our way around each island. The longest wait was around 45 minutes for Dudley Do Right.
One morning, I took the teenagers in our party earlier than we arrived the previous days and headed over to Dueling Dragons immediately. We were able to ride DD in the front row three times consecutively and then went back and rode it again (well, me, one more time before I became nauseated) four more times before the crowds made longer waits.
We used express pass maybe four or so times. FOTL should be great and if you can swing the price of the hotels, why not and skip all the lines? If you want to save money, it sure is doable without FOTL perk.