the first time is so exciting! what am I saying im into the hundreds on hatches and I still get excited. so many things can affect a hatch, but my sebrites are always in the latest of my bantams (typically day 21) in most cases they take about 4-6 hours to hatch but ive seen them take 24 hours. resist the urge to help them, you typically do more damage than good. while they are hatching leave that incubator closed, opening it causes a drastic loss of humidity and can dry out the hatch sticking the chick in the shell.
if the bird never pip's out it may be missing its egg tooth or just to weak to do so. this is probably not your fault so don't get discouraged. if its missing its egg tooth and you were to help it out, its offspring runs a risk of the same problem. so again, do not try to help it out.
im just an email away if you need me.
best of luck,
brian