One of mine took 36 hrs last week.about put me under............
And out of 10 eggs..9 were peeping at me when I candled at day 18.......
I get a lot of cleaning done when this happens..........
Rocking is the FIRST stage, then a pip (small hole in the shell, sometimes it is hard to see since the shell stars out but doesn't actually fall out), then comes the beginning of zipping (where they turn and peck the shell from the inside all around the top) then and only then will it hatch.
Do NOT open the bator, this can cause harm in one of many ways to a chick trying to hatch. Good luck with your hatch.