Use 24-hour clock format

It is currently not possible to show time in Military Time (24-hour clock).

However, by using your locale settings, you can control the way the dates appear. Please note that this also affects the order of first and last name on Name fields.

Here's how to check your Locale Settings:

Classic: Click your name > click Setup or My Settings > Personal > Advanced User Details > look for the field "Locale"
Lightning: Click your image > Settings > User Details > look for the field "Locale"

For example if you change your locale to "English (United Kingdom)" you will see the time in Military format however your dates will appear as DD/MM/YY.

The Locale setting also affects the first and last name order on Name fields for users, leads, and contacts. For example, Bob Johnson in the English (United States) locale displays as Bob Johnson, whereas the Chinese (China) locale displays the name as Johnson Bob.

Related article: Supported Date and Time Formats (ICU)