Your lamp has a built in timer with a 16 hours on and 8 hours off cycle - it's the perfect amount of light for faster growth. Try to make the lamp mimic the natural day cycle: just plug it in in the morning so the light would be on during the day and it will automatically shut off in the night time once the 16 hours is done. It is important for the plants to enjoy some rest in the dark - they need sleep just as we do.
The cycle starts from the beginning every time you plug in the Smart Garden.
If you wish to reset the timer you should always wait for at least 10 seconds after unplugging the lamp to plug it in again. Should the lamp's automatic schedule malfunction, leave the garden unplugged for at least 2 hours before plugging it in again.