There's no bad time to visit Crete, but the best time to go is in May. The weather is perfect at that time of year - not too hot, and with just a hint of a breeze to keep things comfortable. The island is also relatively quiet in May, so you'll be able to enjoy all of its attractions without having to fight the crowds. And if you're looking for a bargain, May is the month to find it, as hotel prices are lower than they are during the peak summer season.