Military Time
https://military.onlineclock.net/chart/
9:00 a.m. 0900 or 0900 hours "Zero nine hundred hours" 5:00 p.m. 1700 or 1700 hours "Seventeen hundred hours"
12:00 a.m. is usually referred to as both 0000 and 2400 hours. Clocks which can display Military Time, however, always display this time of day as 0000 (and not as 2400).