If I understand your question, since you are on this site as a buyer...you wrote an offer and the seller signed it on 7/30.
Now if it's a "normal" sale, the contract will have contingency dates for deposits, inspections, mortgage committment...and an "on or before" closing date. If you are using an attorney, and a Real Estate agent, they can explain it to you. Typically from contract date to closing date is between 60-90 days.
If it's a "short sale"...forget all the rest of the mumbo jumbo about who signs what...bottom line is, once the contract is signed and submitted to the bank, with ALL the necessary documentation.... it's ultimately up to the bank to approve the sales price.... AND it can take MONTHS !!! I have seen many a contract closing date come and go while waiting for the bank to approve the short sale.
Again, if you are using an agent and/or an attorney they can explain your rights and obligations regarding the contract.