When I filed for a fiance visa in 2003, there was a delay. After the approval, the packet went to the National Visa Center to get checked for security, then it gets sent to the consulate.
I don't know about China, but in Mexico, it was the same day for us. But, she had the medical exam the day before. Day 1, get the medical exam. Day 2, spent almost the entire day waiting in lines. The visas were issued, but they made a mistake -- we had to spend the next morning waiting to fix it.