Jammer, I think that is Inyo's intent -- that you can hang out and keep checking for slots to show up, using "your own device". They intend for no-shows to appear on the web, too, but are still hashing out the timeframe... they don't want a flood of slots to all appear at once, instead they want them to show up at random times. The time window is still being worked out.
This applies to both Day Use and Overnight use on the Main Trail, (and Day Use on the Mountaineers non-trail Route, since it requires the same Day Use permit).
They want to extend this process in the future to the walk-in and no-show permits for all the other trails. I just don't know how it could extend to the Trail Crest Exit Permit, since that permit requires that you first get an entry permit on another trail. And also, those walk-in exit permits are given to people picking up their trailhead entry permit when they pick up that entry permit.
