One night probably won't cause hermies, but it's wise to keep a close eye out for them anyway.
AND...
It will most likely slow the maturing process, as the plant will probably revert temporarily to a veg state. You could be looking at a 1-3 week delay.
psteve Reviewed by psteve on . would 1 nite of lights on hurt when in 12/12?? left my cloning area open thats in the same room as the rest of them but forgot to seal it up for the nite so the 12/12 had lights on for the overnite 12 cycle how bad would/does this hurt?? Rating: 5