I agree with wbtravis, just show up. I got an overnight main trail permit for two last Saturday for entry on Sunday if you can believe that, and mid-August is much more popular than mid-September. Note there are 3 times of day that are important in terms of getting day of issue or no-show/cancellation permits: 8:00 am, 11:00 am, and 2:00 pm. The rangers conduct a little mini-lottery at those times for the hikers who are present at those times and looking for permits. The permits given out at 8:00 am are for same day entry, the ones given out at the other times are for next day entry. So plan your arrival in Lone Pine accordingly.
