The caller on the call that captured the screams said the screams happened before she called 911. I think an estimate of 15 seconds to hear the screaming beginning, to picking up the phone to call, to being connected with the operator to be reasonable. Its possible it was a few seconds more or less, but clearly longer than what was captured on the 911 call.
I've read several articles saying Cutcher and Mora heard screams for help. On looking back at those articles, it says the witnesses heard screams for help, but when quoting Cutchers words, it does just say she heard screaming or a child crying. That at least some of the words were "help" is fairly easily discernible on the 911 call. The more important point was that neither Cutcher or Mora mentioned that they thought the screams were from a child until their media interviews and if they thought a child was calling for help for a minute, why didn't they do anything? She made comments about certain things she sure didn't happen because they would have easily heard them, so she was either making that point up or could hear the screaming quite clearly. I tend to think its the former and they didn't really hear the screams that clearly and their media narrative was enhanced for whatever reason.