I did it and my plants turned out fine, I like the 18/6 schedule better because it seems like it makes the plants hardier. I just turned them off one night at 11 (after I bought a timer) and set the timer to 6 hours now it shuts off at 11 everynight and starts up at 5. I would suggest getting a timer to make sure they shut off and turn on everyday at the same time to reduce stress.