When to switch to 12/12? The plants are about 10 t...

I would still wait , based on what i see in your pictures your plants can go for another little bit in veg . I would only think about switching them ones you see your calyx with hairs stick out form this is what we call pre flower and that means your plant is displaying signs that its mature enough to start flowering . That don't mean you can't do it now but its always better to be patient and wait until the plants are ready :) I hope this info helps you a little bit in understand when you should be thinking about switching your light schedule to 12-12 . -Happy Growing!