Time it took to hit the bottom...
Does that include the 2 hours and 40 minutes on the surface?
It was traveling at 20 knots going down to a spot 12,500 feet (about 2.5 miles) below the sea....
According to google calculator, that's 23.015589 mph....
Using the calculator again, it would take 0.102861771 hours, or just over 6 minutes for the BOW. The stern fell faster, as it fell almost vertical....
In all, I'd have to guess, oh, say, about 10 minutes of falling between the two pieces, giving the stern 4 minutes?