VFR,
Was that the incident where a Cessna flying the other way happened to be looking at him when his engine went, saw him hit the water and subsequently dropped him a life raft ? I recall reading that he had an immersion suit on but the zip wasn't quite done up and he reckoned he nearly died due to the cold water coming in through the 1" gap sapping his strength, such that he could hardly climb into the raft. Very, very lucky the Cessna was around. And top notch thinking and flying (and bombing!) by the Cessna pilot.
As for how long the things float, I should imagine it would depend on what doors/vents/windows are open, closed or smashed. But seemingly, not long.