Samsung
Switch Between 12-Hour and 24-Hour Time Format auf Samsung
Samsung's One UI defaults to 24-hour time on most devices, even when the phone language or region normally uses a 12-hour clock. This setting is tied to the system-wide date and time configuration, not to individual apps, so it changes the clock everywhere at once: lock screen, status bar, calendar, and alarms.
The toggle sits under a single dedicated option, separate from automatic time zone settings. Switching it does not affect automatic date and time syncing or your selected time zone, only the way hours are displayed.
Menu path
Tap on Settings ➔ Tap on General management ➔ Tap on Date and time ➔ Enable or disable Use 24-hour format
Turn the switch off to show times as 1:00 PM instead of 13:00, or turn it on for the 24-hour display. The change applies immediately across the system, no restart needed.
If the option is greyed out, automatic date and time syncing is usually the cause. Turn off automatic sync first, then the 24-hour toggle becomes selectable again.