There would be so many things that would have to go exactly right.

First of all, even if you had the use of your flaps, you would be touching down at maybe 100-150 knots. You would like to have very favorable sea conditions (small waves) and a headwind. Even ditching a Cessna in calm water risks severe injury to the occupants as the aircraft can break up or flip upside down. Assuming the jetliner managed to ditch with the fuselage more or less in one piece, who knows how long it would stay afloat or if the rafts could really be deployed. You would need very warm (80 F+) water to avoid one's succumbing to hypothermia before any rescue could be accomplished. In most seas the temperature would be far from ideal, in icy waters you might have 5 to 15 minutes, tops. Only then do you begin to address the question of how long it would take for rescue ships/helicopters to arrive.

Fortunately, with GPS-equipped satellite EPIRBs, it's "No Search, All Rescue."