Agree with the RubyNala, once they start a full zip, an hour total is about my maximum. They may stop for a few minutes between turns, but once they start, they should continue. Some breeds tend to be worse about starting and stopping than others.
Another thing along that line is skipping sections of shell while zipping. They shouldn’t miss spots, it should be a nice clean zip. But if random spaces get missed, they could have trouble once they get around. I usually pull the cap off those too, then let the chick finish pushing out.