I have days i can go as sept 27,28,29 or 30th of sept. I would think the odds of securing a permit , late in september , could be a lot greater than this month.
So you are looking for a day permit for the last Tuesday, Wednesday, Thursday, or Friday in September. Based on last year's data, which is
here, there was a huge glut of unused day permits on all the last days of September (approximately 20 or more permits not used on all those days). So your chances are very very good based on past experience. Indeed, after September 18 last year, you would have scored a walk in day permit ANY day of the week through the end of October.
If you want to maximize your chances, go up September 27 to try to get a walkin permit to enter early in the morning of September 28, and if that does not work (though it should), ask if they will give you one to go up September 29. (Or, you could try to get an overnight permit as an alternative.) But I bet you get a day permit the first time you show up at the office.
If it were me, though, I would go midweek in August. Longer days, better weather. As you'll see from the same chart, they had more day permits than takers every single weekday in August ... meaning that anyone who walked in for a day permit midweek in August got one. And there was a significant glut at the end of August. It's only on weekends in August that there was a struggle.
