make sure you ask them how will they remove it without damaging the defroster. They should have 1 of the 2 methods, Steam or Ammonia. Steam will take a bit less time than ammonia, due to the fact that the ammonia method will depend on how sunny it is and also how warm the day is. I've had it done with a shop that uses the steam method and my defroster works flawlessly. Hope that helps.
Rob
It's never "DONE", just finished enough to drive :-) - BigTDogg (MA)