We had an accepted offer from the sellers on January 18th, 2008. In late February, the BPO was ordered and two weeks later we had word that it had been received by the lender. We didn't close until April 11th and I'm pretty sure it only happened that quickly because we were already two weeks past all of our contract expiration dates and we told the lender that we were losing our mortgage committment. Since the interest rates had increased by almost a full point since our lock-in, our monthly payment would jump by about 10% and we weren't interested in the house at that price. Also, we were in probably the best position for a short sale in that the house we were trying to buy had received no mortgage payments in 12 months, had 3 foreclosure auctions postponed due to various stalling techniques by the sellers, the sellers had declared bankruptcy and we had no contigincies on the purchase (other than a must-close-by-date).
Good Luck! If the sale goes through and you love the house, it will all have been worth it!