We stayed May 19th - Jun 1st, and had more rain than all other visits over 15 years combined. It was torrential on a couple of days, although not for too long, particularly over the last weekend.
That said, it was 'sort of' quite nice to just sit and relax rather than deciding what to do, and except for Sunday the rain wasn't continuous and we had some sun. Leaving this morning, it was getting too hot for us, heading towards 30C.
We also took advantage of the BA chaos last weekend to obtain a refund and stay 2 days longer than we'd planned - our apartment at Skinos was, by chance, available, and we had two lovely sunny days this week, which were not too hot, and a pleasant breeze to boot.
Richard