I don't know why they call them short sales when they usually take 3 to 5 months to close. lol
Some circumstances warrant extra time such as an IRS Tax lien that will take time to get released or are lien holders that the negotiator is working on signing a release from the property.
If the lender is the hold up, they are possibly just overloaded with too many files.
It depends on you more than anything. You should get enough information and then make an informed decision that is best for you and the seller.
I'm not offering legal advice here but just sharing what I would do if it were me:
If you put up option money with the seller you will very likely lose it. The option money would go to the seller or could be held in escrow. I would not the seller more than $10 or so for an option unless you put the option money in escrow with an attorney. If they are being straightforward the $10 should suffice. If they want more under these circumstances, I would be suspicious.
If you move in I would insist on a reasonable rent amount and lease term that is suitable and probably not just month to month. I would want a term long enough so that it was worth my while or the short sale was approved.
You can stack the odds in your favor. Consult an attorney and have them explain the risks, review all the documents and answer any questions before a final commitment is made.