If your offer is a good amount lower than either the prior offer or the BPO, then it will likely be longer and up to 45-60 days. The negotiator may reject your offer. But if a significant amount of time has lapsed since the BPO was done, they might start the approval process over which starts with ordering a new BPO.
Best of luck!
San Diego Real Estate Specialist
Residential Sales and Appraisal