Tricia, where are you entering to have such a short trip?
The quota for exit permits is 25 per day, and 40% (10) are held for walk-in requests. Walk-in requests for trail entry permits are normally made available the day before the entry date. However, I just don't know how they handle the 10 walk-ins on the exit permits, since the day before, all those who could use the permits are somewhere on the trails.
You should call the Wilderness Permit Office at 760-873-2483 and ask when and how those walk-ins are made available.
Ask about noshows, too. People often get reservations 6 months in advance, and then they can't make their trip, or some members drop out. These people often do not modify their reservation until they show up to get their permits.
And finally, watch the online system in the final two weeks before your trip, as sometimes good people WILL log in and drop their reservations.