ProPresenter supports displaying clocks using the 12-hour or 24-hour format. By default, all clocks are shown using 12-hour.

In order to change this you will need to open Clocks and Timers, which is not part of your default Toolbar. You can access this feature under the View menu.

Once you have Clocks and Timers open, check the box next to "24 Hour" to switch the clock display format. You can use the box immediately to the left to add seconds and your time zone abbreviation to your clock as well. ProPresenter does not currently support Year-Month-Day or Day-Month-Year date formats.

These settings will affect all clocks and timers shown in Messages and on Stage Display.