The short sale process is never sped up because of any one thing. It depends on the banks policies - good or bad - and their procedures - usally pretty bad. Also in play is the mood of the bank's negotiators, plus the diligence, quality, patience, stamina and incredible good work, of the listing Realtor - and a buyer's sheer good LUCK.
The long answer: I have had successes and also bitter disappointments working with banks on short sales. I've had them close in 6-8 weeks. But more commonly is this experience: on one home, I submitted three different contracts and the bank took months to work each one. Each time the buyers waited patiently and each time either the bank turned the offer down or the buyer simply got tired of waiting. Guess what? After one and 1/2 years of trying to short sell the home...that home is now 2 years empty. The seller and I just gave up trying to work with the bank (Countrywide, btw). Now it is going into foreclosure, and overgrown by weeds and bushes, i.e. a once great house is now an eyesore in the neighborhood and will probably be empty another year or two...given how slow the banks are doing anything now. It will probably sell for so much less than any of the offers I brought the bank, that you have to wonder what the banks' real agenda is when it comes to short sales.
The short answer: I have had "bank approval" and still the banks turned down the offers AND took months to do so.
If you have patience, and a gambler's constitution, you may well end up with a great deal. There is NO telling.
If you have any kind of time frame to work with, then a short sale is not for you.
The good news is that in this market, most sellers are having to compete with short sale and foreclosure prices. Honestly I think you are better off having your Realtor find you either a seller owned home for sale, or a foreclosure. Short Sales are just a mess with no sure conclusion at the end of the deal.
Clearly I am one Realtor that is OVER short sales until the banks start treating buyers with care and respect. The National Association of Realtors is working to get the Banks to stop being huge impediments to our coming out of the housing crisis.
BTW, the banks treat Realtors who are trying to do these transactions extremely BAD for the most part. They don't respond, they don't seem to care that we are working for families and they certainly don't want to pay us for our work.
But other than that, I don't really have an opinion ;-)