Why do health care settings use 24-hour time? A. Health care settings actually use 12-hour time, not 24-hour time. O B. Each time occurs twice a day, but using the a. m. and p. m. abbreviations prevents error. O C. Each time only occurs once a day, which leaves less room for error. O D. Hospitals use special clocks that designate all 24 hours in the day separately.