it would be ok if you just give it a longer dark period and then go back to your 12 hours of light
so you would have to give it a 24 hours of dark, then your 12 hours light, and then back to 12 hours of dark, and so on.
it is better to give it a longer dark period, then a longer light period, cause it could go hermie or send it back to veg.
keep em green