I second that motion.
In Ed Rosenthal's book, 2010 edition, he suggests at least 12 off and an initial extra hour off in the beginning of flowering cycle to
help the process initiate. In my own personal experience, I don't own a timer. I turn lights on when I leave for work at 6am.
I turn them off at 6pm...roughly speaking. I've missed the on part by as much as an hour (extra darkness) and I don't see any
signs of stress at all. I guess it's safe to assume that if you're going to err, you should err on the side of less light not more.