you will probably still have some hatch. ive had temps drop to the mid 60s and still get over 50% hatches. if you open your incubator 15 minutes a day every day during the hatch, it also helps with resistance to power outage. if you don't, the hatch rate will drop but some will still come out. usually when the temperature drops like you are explaining, you will have more pullets hatch. supposedly cockerels are killed by the spike in temperature.