Mine usually pip on day 19, but I've only had one baby sucessfully hatch without assistance. On day 18, I raise humidity to 70%, then My rule of thumb is that if I see a pip in the shell( day 19, or 20) I mark down what time pip occurred,(chick should audibly peep back at you at this point) wait...
Serama and silkie lover- Have had great success hatching Serama eggs, but ALL of them have to be helped out after pipping... Very different from other chickens, I've only had 1 successful unassisted hatch, so If 24hours has passed after pip, contrary to most information regarding incubating...