Few weeks into flowering. 
2 weeks into flower?
Are you keeping notes? Good to write things down for future reference.
I’d say 2-3 weeks depending on stresses that might impact autos timing.
Yes I’m keeping notes
Thank you
When should I change my Light Schedule 12 on12 off
you’re growing autos, right? No need to change to 12/12. Wht are you running now?
I’m running 18-6
If they’re autos (which I assume they are based on the fact they’re flowering and you’re on a 18/6 schedule), you don’t need to change the schedule as @PP3121 said. I ran mine 20/4 until flower. Then for the hell of it, switched them to 18/6. I’ve read that the darkness helps um develop during flowering? Probably a myth but I went with it lol. Either way you go, it won’t hurt them. You can do 12/12 just to save on your electric bill but it’s not necessary.