Denwa Communications DW-820 User Manual page 43

You can increase or decrease the corresponding value by dragging upper or lower,
also can directly input corresponding value in input flied, and then click the "Done"
button.
Click "Set time, time settings, as shown below:
In the figure, uncheck Use 24-hour format, you can increase or decrease the
corresponding time value by dragging upper and lower. Click "AM" button, it will
change to "morning", and then click "PM" button, then changed back to "afternoon".
If check Use 24-hour format, time setting interface as shown below: