1. There can be more than 1 lien on the home (i.e. 80/20 mortgage, HELOC, water) If 2 mortgages they may be with the same bank or different banks, if different it can take longer to get them to agree on the settlement, if they will agree, some will never agree.
2. Even though the mortgage is serviced by a bank that doesn’t mean the primary investor is that bank they may need to take the negations to another bank to see if they will work with it. (Typically this is how Fannie or Freddie fits in) as they are the primary investors in the majority of loans.
3. There may be defects in title, or legal disputes such as property lines etc... That may be involved that can hold the process up.
4. The Realtor or third party negotiator that is working on the file my be very experienced and have connections or not. This can vary the time of a short sale by over a month or two.
5. From the time you make an offer the short sale times can differ if the sellers have already started the process with the bank, compared to starting at Square one.
I guess what I’m trying to convey to you is that they are very complicated, and can be simplified if things are be handled by professionals. I have had probably close to 40-50 short sales completed in the last 2 years. And they have ranged from 45 days to just over 10 months. I would say a typical short sale should take around 3-4 months. You should look the professionals you are working with to give you an indication of how long you individual situation is going to take, and the variables involved.