I ALWAYS candle on day 18 before I up the hum, that way if there are any "dud" eggs or babies that didnt make it they dont screw up the other eggs by exploding or anything !!!!!! So on day 18 candle quick and then up the hum !!!! Just keep in mind that on day 18 if you dont see alot or any movement in the egg doesnt mean they are dead, its hard to see movement that far along !!!!!