It will vary from publisher to publisher and topic to topic. If you wrote a quick-turnaround book on a hot current-headline topic, it could be out within a few weeks. It's more likely to take between a year and 18 months.
My proposal was accepted in Aug. 2001. I turned in the final manuscript in Dec '01/Jan. '02. The book hit the shelves in February of '03.
Note that I didn't have to do additional rounds of editing -- just one pass from the editor and one from the copy editor, both returned within 10 days. If more extensive editing had been required, the date could very likely have been pushed out further.