hey SubL,
Steve C posted this link to last year's un-used permits.
http://www.whitneyzone.com/wz/ubbthreads.php/topics/135#Post135

If you look at September, you will see that only three days had no un-used overnight permits. That means that on any given day in September you have a 90% chance of just walking in and getting a permit. Of those three days, all of them were either on a Friday or Saturday. In other words, if you are looking for an overnight permit and you choose a day other than Friday or Saturday as your start day, you are pretty much guaranteed to get a permit.

For a day hike permit in september there were only 5 days that didn't have any un-used permits. That works out to about 84% chance of getting a day permit on any given day. But again, all 5 of those dates that didn't have any un-used permits were either a friday or saturday. So again, you are pretty much guaranteed to get a permit if you pick a day other than Friday or Saturday.

I'm planning my hike for tuesday Sept 7th. i don't have a permit yet and it is a week away.