To get a better "guess" on how long it may take just for the underlying lender(s) (a Home Equity Line 2nd mortgage adds further complications) to do their independent appraisal of value to determine if your offer is an acceptable price, you will need more information from the listing agent. Also there are some "scams" where the short sale is intentionally delayed so the homeowner can live rent free longer or can collect rents from a tenant longer.
You need a well qualified Realtor to continue to show you properties until you get the approval letter in your hand.
There is no right answer to your question, but typically, you should have an answer within 30-60 days. It is a very frustrating experience for a buyer and the seller who want s to sell their home. Short sales should not be so complicated, but most of the time, they are. I hope you have time to hang in there and wait.
All the Best
Dave & Lisa