Happy new year
Hung PhamCo-founder, 9ThemeStore

Step 1 Log-in to back-end of your site.

Step 2 Go to "Components -> Kunena Forum -> Configuration" menu.

Step 3 Click the "Fontend" tab, scroll down mouse. You will see the "Message Time Format" option. Choose a time format from dropdown.

Step 4 Save and back to front-end and reload your forum.