A lot of people prefer a 12-hour clock with an AM/PM indicator.
If you right-click on the clock and choose “Date & Time Format”, it tries to start a control panel module called “rscp”. Unfortunately the module does not exist, so nothing happens.
Instead, you can change the format yourself by editing the file:/home/user/.kde/share/config/kdeglobals
Open your console and type:
Hit enter. This will open a new text editor. Scroll to the bottom of the file and add the following two lines:
[Locale] TimeFormat=%I:%M:%S %p
Save, exit and re-boot
Another note: It appears that this change only works if your clock type is set to “Plain”. If you have set it to “Digital”
See Changing the Time Format to AM/PM in Easy Mode.
This section is just here so that people searching for '12 hour time', '24 hour time', or 'military time' will find this article.