The fuselage of a jet airliner is a closed cylinder filled with air, and the wings are filled with fuel, which is lighter than water and tends to float.
As a result, the chances are good that the airplane, unless severely damaged, will float, rather than sink. They have been known to float for days, and to be salvaged completely.
Your air crew have all been trained in the best way to handle the unlikely event of a water landing. If the airplane is controllable, it stands a good chance of being belly landed gently enough to remain afloat for an extended period.
Of course if your airplane is hit by a missile or involved in a collision, it may be so damaged that it will sink rapidly. If the fuselage is torn open, expect to sink. In most situations in which the airplane will sink, the passengers will already have suffered fire or explosion.
that depends upon if its "flying" to the bottom or not.
how deep is the lake or ocean....if it sinks at say 100 ft/minute and the lake is 100 feet deep then 1 minute.
if its the ocean and the spot near the titanic (~3000 feet) about 30 minutes. lless if its "floating" like a leaf.
faster if its nose down "Diving" to the bottom.
What a tragic mind you have... Hopefully the plane hits the side of a mountain instead...
The plane will sink quite fast, particularly because it will break up upon impact and fill with water. Most will die before it even submerges.