There is no set time, because it will depend on many factors. For one, if it is a short sale, the timeline is entirely dependent upon the bank, how busy they are, where they are in the short sale process, and how many offers they are reviewing.
If it is not a short sale, there may still be numerous offers, which will have to be reviewed by the agent, as well as the sellers. Then, you have to factor in the possibility of the sellers being out of town, or unable to review them for other reasons.
Generally, you will ask for a three day response, which you may or may not get, especially in today's market! It is hard to wait, but it's kind of inevitable!
Best of luck to you, and please let me know if there is anything I can do to help you!