The world operates on 24 hour time. There are 24 hours in one day.

Many parts of the world break up the day into two lots of 12 hours (AM & PM). From midnight to midday it is AM and from mid-day to midnight it is PM.

The link below shows how the 24 hour time is converted to AM & PM.

http://www.onlineconversion.com/date_12-24_hour.htm