How long does it take for a diver to die from an air embolism?

A diver may: Actually surface unconscious or become unconscious or demonstrate other neurological symptoms within seconds of surfacing. Extent of injury and interventions (if any) will be some of the determining factors regarding death. With rapid intervention - a diver can be pressed in a chamber and sometimes achieve miraculous results.

An air embolus...: Can kill instantly if big enough, and this can happen immediately upon ascent (before surfacing even.) usually, however, it's multiple small bubbles causing intense pain and confusion.