The LEDs are PWM controlled so the brighter LED represents logical 1 and the dimmer one means logical 0.

Excuse my photography skills for not being able to reproduce the exact reality image and brightness of the LEDs as you would see them with the naked eye.

The picture below is explaining how to read the BCD clock. 

To set the clock, press the “S” (set) button for at least one second. The clock will display and highlight only the minutes section. In this state, press the “M” (mode) button to increment the value of the minutes. When you finish setting the minute section, move on to the hour section by shortly pressing the “S” button again. This will highlight and display only the hour section. You can increment the hour value by pressing the “M” button. The “M” button can be pressed continuously for automatic fast increment, or step by step for slow increment. When you finished setting the hour section, you must press the “S” button again to return to the main screen and displaying the clock. This will also reset the seconds area and the seconds value to zero.