If days are in the 80s, I'd just whip the tops off. Just keep something around to throw over them if those colder (frosty) nights are forecast.

Martha

I start opening about when temps are steadily in the mid 60's or higher for any containers I have in direct sun. It gets much warmer in the containers at those temps. I like to keep my seeds in cups inside of zip lock baggies so I can either just start slicing holes in the zip locks or open them. I would still keep them covered at night though until it's consistently 40 or higher. :)