I'd go for May and June for the best diving conditions. As for pica pica they will be there in May I'm not sure about June. I have heard good things about SafeSea. It's a protectant you put on like sunscreen in fact they make some that has sunscreen in it. I have not tried it but when I dive where there are pica pica I always slather on plenty of sunscreen and it seems to work. As Gaz said, bring vineager or windex for relief on the boat, but they won't do a danm thing about the rash you'll have for a week or two after. Have fun and dive safe, maybe We'll see you in May.