If a person is in 28 F degree water then that is pretty cold water and the persons core body temperature would drop pretty quickly if you don't get out of the water.
Hypothermia sets in once your core body temperature drops below normal which is 98.6 F and when your core body temperature drops to 95 F that is when hypothermia sets in and then if you don't get out of the water and get warmed up then you could die.
Expected survival of a person being in 28 F degree water is between 15 to 30 minutes.
When your body loses more heat than it can produce then you eventually die.
So it's important to get help or get out of the water if possible as soon as possible to avoid death.
If a person falls into a body of cold water then they usually die of hypothermia instead of drowning.