How to change time display to 12h time format in Ubuntu

There are several ways:

1. From GUI (Settings):

   Open Settings >Details> Date & Time. Then pick either 24 hrs or am/pm

2. From GUI (using dconf-editor)

   Open dconf Editor (not installed by default, run

   sudo apt install dconf-editor
   

   to install), and browse to org > gnome > desktop > interface > clock-format, and change the format to '12h'

   

3. From command line:

   Run the command:

   gsettings set org.gnome.desktop.interface clock-format '12h'   
   

   To revert:

   gsettings set org.gnome.desktop.interface clock-format '24h'
   

To run the following commands, first install the dconf-editor package:

sudo apt install dconf-editor

Then run this command, to switch to 12-hour mode:

gsettings set org.gnome.desktop.interface clock-format '12h'   

If you ever want to revert to 24-hour mode, you can do so by running:

gsettings set org.gnome.desktop.interface clock-format '24h'