There is no way to know when a chick will pip. There are too many variables that will affect the hatch times, biggest being temps. Generally if conditions are opitmal you see pips and hatching day 20/21, but it can be as early as 19 or as late as 22 (note: chicks can hatch before or after, but the healthiest generally hatch closest to these times).
It's possible to see moving in eggs at day 14ish as the chicks move to the round end of the egg and again at day 17/18 when they are getting into "hatch position". After this you may not see movement again as they rest and get ready for hatch. I seldom see much movement before the pip.
If you hear chirping from within the egg (before an external pip) you know that the chick has internally pipped into the air cell and generally you will see an external pip with in 24 hours. (Could be two hours, could be 24.) Once you see an external pip it
can take another 24 hours before the zip begins. Again, it could start zipping a few hours after pip or 24. After pip the vascular system between the egg and chick has to shut down, it rests and in some cases it may still have unabsorbed yolk to absorb. Can't rush these things.

I seem to average between 12-18 hours for the majority of my chicks. (I also periodically play "chick music" for them after they start pipping.
Now once they start the zip, it should not take hours. Mine are usually out in 15-20 minutes once they start a zip. (I play the "chick music" repeatedly once they start zipping.) If a chick stalls in the middle of a pip and doesn't make progress in half an hour- it is my opinion that it's time to investigate and help out.