It's not really a release by the INFS, just a matter of conscientious permit-holders calling to cancel or reduce a group's size, freeing up permits for re-sale. This usually happens beginning about a week out from a given departure date. I began calling about two weeks out from my preferred date of 7/15, twice each day since a lot can happen at that office during the course of any given day. I always asked about my preferred date as well as the two days on either side (7/14 and 7/16). I kept getting skunked till finally on 7/12 two cancellations came in for 7/14. Slight adjustment in plans, but well worth it to have firm permits in hand.
The only downside to this is that you still have to pay the $15 reservation fee for each permit. If you wait to walk in and hope for the best with no-shows the day of, and score permits, there is no fee.
Also, don't trust the listing of available permits (or non-availability) on Inyo's Mt. Whitney website. They admittedly do not update this regularly. Calling is always the best tactic.
