I wouldn't worry about it yet. It can easily take a full day for the eggs to hatch after they pip and if the eggs weren't kept quite as warm as recommended it's easy for them to be a day or two late. I've had a couple of hatches that were done before day 21 began and others that didn't start until day 22 (and one that started on day 20 and stretched to day 23). just be patient. If the chick that has pipped looks like it is dried into the shell or if it looks bloody in there, help it out, otherwise, let it go. If you help it out, though, be prepared to take care of it for a day or two until it's as strong as the other chicks will be. I've helped eight or ten chicks since the first of the year and almost all of them made it if given enough time to strengthen up before being placed with their rambunctious siblings.
Good luck!
