For how long does alcohol poisoning last?

A few hours...: ...Or until death, whichever comes sooner.

Depends : If you are truly poisoned, it is a medical emergency associated with slowed breathing, hypothermia and potentially death. A alcohol-naive person may be poisoned at a level of 200 mg%, and that may take 15-20 hours to get down to zero, although people will wake up after it is down below 120 mg% or so. Higher levels (like 300-400 mg%) take over 24 hours to metabolize if they havent killed you.