I left it to 14mo with DD. We were all broken from lack of sleep (waking every 45mins, sometimes for hours, refusing milk and wanting to be rocked in a very specific way by me only) and I was so tired I nearly crashed my car. I was almost hallucinating, DH and I were arguing, DD was miserable... it was horrendous. And CC worked pretty much straight away, we were different people after a few nights of sleeping properly.
Our mistake was doing it so late. I feel like we didn't enjoy her early toddler months because we were as so exhausted. If we'd left it any longer I think I would've broken down entirely. It was the best thing we ever did.
So we did it at 8mo with DS. Up every 30mins, every single night. I could feel things going the same way, plus he would only nap on me, nowhere else. It was upsetting DD, I was covered in bruises and scratches from DS headbutting/clawing at me... So we did CC again. It worked almost immediately for him too (I appreciate it doesn't for everyone).
They are now nearly 9 and 4.5 and neither of them remember it at all. They both love their beds, and only wake up if there's an actual problem.
Good luck OP, I hope you start getting some sleep soon 