Panasonic SC-ALL2GN Operating Instructions Manual page 40

Changing the clock display
You can change the clock display.
∫ To change to 12-hour clock
Touch and hold [DISP] and [2] for at least 4 seconds.
∫ To change to 24-hour clock
Touch and hold [DISP] and [1] for at least 4 seconds.
≥ The factory default is 24-hour clock.
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