switching directly from 18/6 to 12/12 is very stressful and most times is the reason for hermies,.
i start seedlings and veg under 16/8, than when time comes to flower i’ll lower the hours by an hour each week,.. at 14/10 most if not all hybrids and indicas will start flowering,. leave at 14/10 for 3-4 weeks than lower to 13/11 for 3-4 weeks than finish out with 12/12,..
sativas and landraces the flowering starts at 13/11 so leave at that for 5-6 weeks than finish out with 12/12,..
your buds will thank you!