Its impossible for anyone to put a single definitive number on how long it takes one person to create a given animation. so many factors come into play, work flow, tools available, complexity of the movement or scene, speed of the hardware you're using, how buggy the software is etc.

as stated before, the best estimate is "a long time"

If it was easy, everyone would do it because its so darned satisfying taking a static figure and giving it life =)