I had one of these units last year and I never could find a manual that explained how to to adjust the time interval but the timer plastic sleeve can be rotated for different settings. You may want to look at the timer more closely before you install a new one. On the unit I had last year the timer was working OK but the slide for the coins was missing some parts. The model number I had was LDG190S-03 and I sold it to someone who was happy with it.