All cold-frame veggies should be uncovered by May 16th and allowed to be exposed to the air, rain and direct sun.
The third week in May on the East End has traditionally been the time to plant all varieties of peppers --- and lettuce can go in about then too. In fact, after the 21st, it is only a month to the beginning of summer, so therefore no edible plant needs to be held back because of temperatures or available sunlight. It is also perfect timing to drop in your dahlias, iris, gladiolus, Calla lilies, sunflowers, sedum, daisies of any type, etc. as all should do fine.