I realize there are multiple threads about the Mama's Heating Pad set-up. Apologies for adding another. I'm trying to determine answers to some specific questions, and haven't found them yet. I have 18 chicks arriving on or around April 21st. I just ordered 1 12" by 24" heating pad. How many will that service? For how long? How many chicks have people used one of these on so far?