In my experience, it's gonna take the plant at least a week or so to really reach the flowering state. In that first week or so of 12/12, it's still in the vegetative state and is beginning to transition into flowering. I have transplanted before a few days into 12/12 without a problem, though it's definite not ideal. I once transplanted a female about a month into 12/12 from a 6" pot in soil into a drip system with hydroton, and while it suffered a bit of stress, none of the plant seemed to end up being stunted or died as an end result. Make sure the nutrients aren't too much for the plant to handle at this point obviously.