Hello,
We have been to Plakias and the South of Crete a few times at the end of May. It is a very good period.
1) Most of the flowers will still be blooming.
2) It is going to be more than 30 degrees during the daytime. You might need a sweater at night and maybe a raincoat for a couple of hours.
3) All the tavernas and shops are open at this time of the year.
In fact, this is the period of the year that we prefer. It is not too hot and the days are long and sunny.
Have fun,
Hugo