They can hatch anywhere from day 14 to day 18, and I've read on here of people's taking 21 days to hatch. If your temp and humidity is right (99.5 degrees forced air/101.5 degrees still air with 50% humidity for incubation and 65% for hatch), they should take 15-16 days.
I'd would stop turning them on day 13, because the little chicks need some time to get into the hatch position and also they need the extra humidity to break out of the shell easier.