Go back to your regular nute strength if this is the only problem you’re seeing. This is a magnesium deficiency that can be solved with a calmag supplement in a few days. 1ml/L should suffice and keep it as part of the regimen for the rest of the grow. Cal magic or botanicare calmag + both work well. You’ve got no real concerns with moving to 12/12 now even while treating this issue because it’s so common in cannabis. That said, why bother with the stress of it, especially if you want to defo through the stretch. Better to wait a full week, see how the plant responds and then flip the switch. Hope it helps homie - u got no issues here that aren’t easily rectified. Good luck!