Usually it takes 8-24 hours for a pip to zip. Usually pips that you think are only a couple hours have been pipped for quite a while and were just unnoticeable. My chicks average 12-18 hours from pip to zip. Unless there is cause for concern, such as yellowish/brown leathery membranes around the pip hole, blood at the pip site, a DEFINITE sign of distress from the chick, you should not interfere for at least 18 hours. Many chicks take 24 hours or more to go from pip to zip. Some chicks take longer for the vascular system between chick to egg to receed. If you try to hatch them out before this is complete you will most likely cause the chick to bleed out. And then, if you do decide to "help" it should only be to the extent of widening the pip hole to check on the chick and the membranes. If he is in the correct position and is not failing to thrive you should moisten the membrane wrap a damp paper towel around the backside of the egg and place him back in to finish the job himself. Anytime you are assisting and there is bleeding at the membrane you should cease and replace the egg with moistened membrane/towel to the bator.