How fast does Narcan (naloxone) typically work?

Depends on how given. If given intravenously, it works literally in seconds (10-20 seconds to start working, works fully in couple minutes); if given intramuscularly (im) it takes 2-10 minutes to kick in. If given in a nasal spray (which is being used in several communitites to help addicts and their friends treat od) it works in-between IV and im, starting in 1-2 minutes, and taking full effect by 5-10 minutes.
Really fast. If Narcan (naloxone) is given IV to overcome an opiate od, the effects are almost immediate. If it is given im the response is slower.