How fast is too fast?

Users like apps to be fast. Many apps use animations to "smooth" the experience. If an animations are too slow, the app feels...well, slow. But if the animations are too fast, they may be so fast that they make the app feel "choppy" or appear as if there is no animation at all. So how fast is too fast for animations? How fast can an animation or transition be without looking too choppy or instantaneous?