--meaning one has all the nutrients necessary, the damaging process is gone, and there are no other problems, the figure of approximately 1mm a day has been bandied about by a lot of research neurologists.

Nerve fibers tend to regenerate more slowly than just about any other bodily tissue. (Myelin sheathing tends to return somewhat faster.)

One can see that if one has damage to longer nerve tracts--say, sensory tracts that progress from the lumbar spine down to the feet, for instance--regeneration may be measured in years, assuming it is complete (much nerve recovery is patchy, and not in the same pattern as it was originally). And sensory nerves, especially, may produce all sorts of weird and painful sensations (parastheses) as the fiber growth cones fight through other tissue on their way to their targets.