You can set your phone to update the time, date, and time zone automatically. Automatic update is a network service and may not be available depending on your region or service provider.
Tap Settings > System > Date & time.
Switch Use network-provided date & time on.
Switch Use network-provided time zone on.
Change the clock to the 24-hour format
Tap Settings > System > Date & time, and switch Use 24-hour format on.