I call it off after mama decides to leave the nest with the others, usually 2-3 days after the first chick. I've never done an incubator. But I'd probably candle, listen for any peeping, and then throw them out if they didn't seem to be doing anything after another day or two.
What day did you set? I would candle the eggs first and look for movement or active veining. If you see no movement, I would do an eggtopsy instead of just chucking. Just in case a baby is still alive.