The best answer is to ask your REALTOR. Each and every case is different. When there are 2 different banks, there are 2 different methods and 2 different timeframes. Then they both have to agree!
I have seen it take up to a month just to have the file assigned to someone at the bank and then another 3 months to get to a closing, and that is fairly common.
There are changes coming that will help in some cases in the future, but for now, you really have no control in the way the banks process short sales.
Did you REALTOR put an expiration on the Short Sale Addendum? That won't hurry the banks any, but it will give you an opportunity to cancel the offer if they take too long to respond.
Be prepared for at least a 2 month wait for approval and then possibly another month to get to a closing.