last year my crop saw a few nights of cold...down to a crazy 28f!
but they warmed up in the noon sun... nice and purple, but they still finished up fine.
i left them in the ground till nearly 2 weeks after the cold front and cropped on time no problems! a few nights wont hurt much... unless they are enduring harsh winds, rain, or snow...unprotected. just watch them carefully, if you notice any scary rapid changes, pull em.
good luck bros!
cheers