It doesn't really matter. Switching to 12/12 is fine.

If you are worried about herms, Dutch Master makes a product called "Reverse" that you spray on your plants in week 1 and week 3 of flower and it kills any male flowers present. I used it on my second grow after having a rogue herm somewhere on my first grow and I didn't have any this time. Its only $25 so it might be worth checking out.