The plants will stop metabolizing (growing) at those temps, but the temp isn't cold enough to freeze and rupture cell walls on the plant. If only for a day or two, push through it if you have to, but prolonged weather like this will really put a damper on your harvest. Speaking of damp, with these low temps, watch the humidity and check for bud rot. Give your plants airflow and don't leave big buds leaning on other big buds, they produce heat. Heat vs cold = mold.