BPO (Broker Price Opinion) is an opinion of value given by a realtor. Even though it is an opinion, realtors are still liable for the information they give. Close to a CMA, but with a few large differences, a BPO gives an idea to what a home is damaged or repaired, and what it is worth today and up to 6 months out. BPOs do not require adjustments in areas a CMA would, such as beds and baths (several BPOs don't ask for adjustments on these variances).
If the second loan already approved the short sale, remember that it has no bearing on the 1st and the amount of time it takes. If the BPO was of decent quality there normally isn't a holdup, but if it created questions there may be another BPO ordered. It's not always kosher, but try contacting the agent who did the BPO for the 1st and get a ballpark of whether things are looking good or not.