Hypothermia gives the recipient about thirty minutes, before the mind cannot move the limbs, and unconsciousness and drowning are the consequence, The body retracts to the core heat, and if that cannot be maintained.. life stops.
I am not sure if the life jackets of the time were rated for a maximum safety height for jumping into the water. The boat deck of the Titanic, on which the majority of people were in the final 10 minutes or so, was around 60 feet from the surface when the ship was in its neutral position, higher than most other ships of the day. I am not sure what that actually was that night with the liner about 2/3 full with people and perhaps slightly more with cargo. I am guessing that jumping into from 60 feet in those life vests certainly involved a risk of serious injury, even if not a broken neck.I read somewhere that the design of the life jackets could actually break your neck when you landed in the water