I would not lift the lid unless u really need to for example if one has not started zipping 12 hours after pipping, like i sed you can leave the hatched ones in there for a while and any that have pipped shoudnt worry you unless they have made no progress 12 hours after and any that havent pipped could just hatch a day or two later which often happens, or some one may not hatch at all due to a deformity or other difficulty.