Reducing and stopping elavil (amitriptyline) to see if my nerve pain from disc extrusion has eased or is just being masked. How long after stopping will I know??

Not on your own... Do not do it on your own. Stopping Elavil (amitriptyline) suddenly can give you significant adverse reactions which may include irritability, agitation, sleep disturbance, flu-like symptoms and, rarely, cardiac arrhythmia and should be tapered down with the supervision of the doctor prescribing this medication.