Received a bunch of fertilized chicken eggs from a friend. All went into my new incubator. Yesterday, 2 little black chicks emerged. None since. Should I put the ventilation plugs back in to keep the humidity constant? How long can a newly hatched chick survive without fresh air? How long should I wait for the remaining eggs to hatch? 2-3 more days or longer? Should I help them by cracking the shells at this late date?