In Ubuntu 17.10 and later how do I change the clock to a 12 hour format?

In Ubuntu 17.10 with GNOME, how do I change the clock to a 12 hour format? And maybe for a more difficult rhetorical question, why does Ubuntu feel compelled to hide such basic functionality?

2 Answers

Click on Activities and search for "Settings" and launch it. Click on Details at the bottom of the sidebar and then select "Date & Time".

You'll find an option to change the time format.

For an option with more customisations, you may use a GNOME shell extension called "Clock Override" as mentioned in my answer here.

In search bar, search for "Time" and the "Date & Time" setting comes up, click on it and change to "AM/PM".