I didn't apply for the Spousal Visa. I applied for the Fiance Visa in person at the NY office.
We arrived on Tuesday at 9am. I didn't get approved until Monday am, so 5 days later after in person application. However, there was complications with mine. I was denied entry into the UK on my last visit. Even though I had the paper work with me from the airport stating the reasons why and that they had allowed me a 5 week temporary stay, the Consulate still had to verify the information with the airport. From what I understand from the Enquiry line, the Consulate had been waiting on the information from Glasgow airport, and it wasn't received until Friday.
Depending on the complications of your application I would probably expect about 5 business days at the worst?
They were suppose to phone us and let us know by the next day (we were told it would be ready the next day). We never got a phone call. I was notified of approval via email, so be sure you have access to your email if possible, in case they email you rather then phoning (if it takes longer).
Hope that gives you some insight.