typically you don't go backwards like that. If you're in veg state, how far into it are you, how tall is it? I would start it at 12/12 at around 8 inches, it will shoot to about 15 inches in a short time, maybe more if your pot is huge. But, if your pot is huge then I guess wait more like 15 inches before 12/12 time.
You are suppose to mimic reality. As the days go by, months at a time, the declination of the sun decreases and the days become shorter. From May it is about 14 hours and by September, closer to October the days are at about 13 hours. Perhaps only on the equator could it ever be 12/12 but people do that because most plants respond to that timing, so go with that.
not sure what your setup is like, but typically you decrease the daylight over time.
