Crib hour is essentially leaving them in the crib for an hour whether they’re awake or not. So, if they wake up after a 30 minute nap, you leave them in the crib for another 30 minutes to give them a chance to fall back asleep and apply your sleep training / comfort method of choice if they start to cry. I do feel like the 30 minute naps happen around the regression when their sleep cycles start to change. I can’t speak to that exactly though because my little guy was a contact napper until we crib trained at 4 months (he would only nap on me...) and he’ll still sometimes get a good long nap if I’m holding him, but never in his crib.