I'm guessing you don't know how the whole 24 hour thing works...
In the 12 hour(am/pm) version you have AM(before midday) and PM(after midday) as indicator after the given hour. In the 24 hour version you have no such indicators, as the time is displayed between 0:00 and 23:59.
Here is how it works if you wanted to convert:
12:00am to 11:59am = 00:00 to 11:59
12:00pm to 11:59pm = 12:00 to 23:59
For example:
07:45 is the same as 7:45am
OR
13:30 is the same as 01:30pm, as it is past the 12 hour mark.
