It simply depends on the bank and numerous other factors such as:
1) if the loan that the seller has is the original purchase loan
2) has the owner refinanced
3) is the home owner occupied and principal residence or a rental
and on and on.
No straight answers. I would be happy to talk if you would like.
Do you know if the BPO has been done yet? (meaning the bank who is selling the house, have they had their appraisal done on it yet?) Has a short sale package been sent in yet? There are a lot of factors. It depends how far along the listing agent and seller have gone with the bank previous to you writing the offer.
I have seen buyers wait up to 4 months to get answers in regards to a short sale, where as others I have seen answers in a just a couple of weeks.
I wish I could give you better answers. Not to be funny, but there is nothing short about a short sale!
I hope this information helps! Best Wishes!