There is no standard time line that you can count on to expect to hear back on offers on "Short Sales". Each Short Sale situation has it's own unique set of circumstances surrounding the sale and the principals in the transactions differ from sale to sale. Individual circumstances may include unmotivated sellers, inexperienced agents and lending institutions that are swamped with foreclosures and are in the process of being downsized themselves.
The standard answer that I give my clients when we discuss the possibility of submitting a Short Sale offer is that they can expect an answer back in "Two". The answer may come back in, "...Two weeks, Two months, To never"! Having said that, Short Sales can offer buyers a great opportunity to purchase a home below market value. If you are the seller placed in the position of going through the necessity of a Short Sale, the Short Sale can assist you with removing yourself from the negative consequences of a foreclosure. While a Short Sale will certainly bruise your credit, a foreclosure can damage your credit rating for years to come.
My recommendation is to work with a real estate agent that has specialized training and knowledge in the completion of Short Sales. They will have the experience to work through the issues that surround the Short Sale process and to advise you during the course of the transaction.