[Norck]

As on wiki said:

Quote:

Drunk level will automatically decrease over time (roughly 26 levels per second)

and

Quote:

Levels over 2000 make the player drunk

So we got:
(5000-2000)/26 = ~115 seconds
(8000-2000)/26 = ~230 seconds
(15000-2000)/26 = ~500 seconds

Well, that's it.