When it's dry, although you might want to leave it in the incubator for a while still to motivate the rest of the eggs to hatch. The chick can survive on the absorbed yolk for up to 3 days, so it will be fine for a bit longer in the 'bator. When you remove the chick and place it in the brooder, be sure to have water and food at hand for it. A low bowl of water with some pebbles in it to stop the chick from drowning is a good way to go.