Hypothermia is not entirely based on time, but also temperature and the victim's bodily specifications. Hypothermia is a condition which occurs as a body's temperature drops under 96 degrees Fahrenheit, according to The Weather Channel. This is what actually kills the victim, rather than just cold temperatures over time.
Hypothermia is influenced by many factors but the temperature is one of the most critical factors. When temperatures are extremely low, it is easy for hypothermia to set in quickly, leaving a body with less time to avoid exposure. In certain cases, frostbite -- which is the first steps of hypothermia -- can occur in five minutes. Also, a body's size and personal health status can both play a large role into the rate of exposure, notes Climbing-High.com