Take your clones the day before or the day of your switch to 12/12
You take the clones after the switch here are a couple of reasons not to:
1-If plant is in Bud, you will destroy bud sites...
2-Your clone will need to "Re-veg" and it takes a couple weeks
3-You will get really funky weird growth, and sometimes, it don't go back to Veg, normal...