Her police certificate was ready in 1 week, but we had expedited it, since her Visa interview was only a few weeks away.
By the way, make sure your Thai fiancee has his "single status / marriage status" document. It will be needed at the visa interview.
My fiancee said there were a lot of other people getting rejections, because they were lacking necessary documentation at their interviews. Fortunately, we had everything in order and should have the visas within 10 days.