We run 3 Bator's started at different times so there is a bunch of action to keep up with. In our experiences, we get peeps started pretty much on day 20. Day 21 is eventful. Then day 22 we assist by gently cracking a ring around the egg without disturbing the membrane especially on the bottom. The chick needs to absorb the fluid. We tear a little of the inner and out membrane at the peep to give a little incentive. If they are not strong enough to finish the job, they don't but most of the time they make it.
We never had a day 19 chicken peep before. Not saying it's impossible just never witnessed it.
Good luck!!