After topping...

About how long should you wait after topping to go into 12/12?
plants are about 30 days old now and I am limited in height space.
Thanks for any reply.

Wait until you see noticeable growth... that shows you the plant has recovered and you won't be putting any undo stress when you flip to 12/12

PersonalJesus has good advice for ya. Personally, I don't care, if it looks healthy just do it. Lots of plants, lots of time, lots of energy, everything will be alright as long as you listen to your plants individually