Leaving a light on 24/7 not only drives up your electricity bill but also does harm to your cannabis plants because auto-flowering marijuana still needs darkness to rest.
For your auto-flower, 18/6 is a solid option. It is not necessary to start any plants with lights on around the clock.
Additionally, you can and probably should begin reducing your light hours from 18/6 to 12/12 after flowering is fully underway.
MORE: How Many Hours a Day of Light Do Marijuana Plants Grown Indoors Need?