I think YOU dictate the cut-off... when my LO was a baby about 6mos+ we did CC and she never cried more than maybe 5mins max and I only ever had to go back in usually 2-3 times... so it worked well for her (then)- NOW, with the new bedtime issues she's have at 2yrs, I just cannot let her cry for more than maybe 1-2mins... if that... cause she will just work herself up into a frenzy!!! And listening to her scream for me kills me! I know some parent swear by CC or CIO for toddlers- it's just not something I can personally do... so... for now, we spend a big chunk of our evening in her room till she is Ok on her own. Even though it's not ideal- I've no clue what else to try. The couple times we did some controlled crying with her one of us would crack... it's HARD... probably one of THE hardest methods. But, was a great one when she was a baby- just not so much now. But, she also knows how to self settle and did for month prior- so this, I'm hoping, Is just a stage and will pass soon enough...
Sorry, no great help. Do what your comfy with hun. That is all any parent can do.