Your right that the exact amount changes by minutes. But hes talking about changing it completely and messing with the light cycle. Bad idea. My point is still the same even though you felt the need to try and correct me over something trivial. 12/12 is "generally" supposed to emulate late summer/fall sun.
Keep the light cycle 12/12 unless u got the time and money to play around with or want to make it an experiment. My opinion is you will be hurting your yield big time, and possibly getting stressed out hermies and seeds.