One thing that bothers me is that people tend to expect miracles. I usually tell them it will take as long as it took to fuck it up to fix it. But that doesn't mean that you can't have some initial results to point the way in a short time. It's more about establishing a process and showing that there is a way out of the swamp than that it is something super tricky or difficult. Just follow the recipe, don't let yourself be distracted (this can be really hard, some management just can't seem to get out of the way) and keep moving.
Oh, there's no doubt in my mind about that!
Some people may read this and extrapolate too far regarding their own situation (there's a reason this is a specialty field, it's hard stuff).