if the chick external pips the right end, you should give them 24 hours to zip.
if they pip the wrong end (small end)they may take up to 48hours.
The zip should be pretty quick, 15mins-1 hour in my experience. If they have trouble zipping, that's when you should step in.
Most likely they won't...
Depending the ambient humidity where you live, it may or may not be okay to take the eggs out to candle. If humidity is low where you live you will risk shrink wrapping the chick. You can candle all the way up to the external pip without too much concern for shrink wrapping... but be aware of...