This process, working with a bank, can take months. If the bank comes back with a "yes" by Oct. 15th, then you should be able to close by the end of November, to qualify for the 8K tax credit.
I am trying to steer my first time buyers away from short sales as I know the deadline is looming and again there are no answer time guarantees. If you get a positive response from the bank by Oct 15th, you should be ok to close in time.
Good luck the biggest thing about short sales is you need to have patience. It can seem like a long time brfore things start to move.