Hi all. Just signed up for this board as I was trying to reserve a Trail Crest exit permit as well and found this thread while searching online for more info.
Walk-ups aside, it seems like the current TC exit permit reservation system is less than ideal. The exit permits free up a week ahead of the entry permits (meaning that six nights minimum of camping are required), and for the most part all the reservable spots disappear within 24 hours or much less. But as the original post in this thread describes, all the major trailhead reservations disappear within 24 hours as well. The problem is that none of the major Inyo trailheads are a six night camp from TC exit, for most people. Cottonwood and Kearsarge are less, and South Lake and beyond are more.
I have a feeling most people are reserving TC exit permits on a six night itinerary with a faint hope of being able to change them or "work something out", but will not end up using them as neither of those things are possible. The only thing you can do with an "Overnight Exiting Whitney" permit is cancel it completely.
I think a better system would be something like an ongoing windowed lottery that you enter when you secure an entry permit. Something that would make it possible to reserve a 3-4 night trip or a 10+ day trip with equal probability of getting a TC exit timed to your entry.