There isn't a specific time frame. The quickest it can happen is this:
1. Notice of Default (NOD, minimum 90 days)
2. Notice of Sale (minimum 28 days)
You're already past that.
Have your agent (if you're working with one) contact a title company and find out when the NOD and/or NOS has been filed, then see if there is a schedule auction date. You can even get a phone number for the trustee and contact them to get the latest on their timeframes.
There are several factors that can effect the timing of a short sale, one of the most important is the experience of the listing agent.
If you don't have help, feel free to give me a ring or shoot me an e-mail and I'll point you in the right direction.
Tom Goeders, Realtor, SRES
Keller Williams Realty