Interesting. Not sure if that applies to Whitney permits or not.
Not really applicable to Whitney permits, unless someone started at Whitney Portal, and hiked over Trail Crest and camped on the other side (in Sequoia N.P.). There are a number of Inyo N.F. trails where people start out on an Inyo trail head, and cross the Sierra Crest. It is the trail head agency that issues the permit for the entire trip.
The part about exiting the wilderness for 24 hours is mostly for long-distance (like PCT or JMT) hikers who need to come out for a resupply. They can spend the night in town, get their new supply, and return to the same trail, on the original permit.
I suppose someone could sort of live in the mountains on one permit, coming out every week or so for new supplies. As long as they moved their camp location at least once every two weeks, they could spend an entire summer in the mountains, on a single entry permit.
