Okay I found why my system don't work, len expression detects how much characters the typewriting text will have from the beginning, where it detects current lenght with the addon I use, I think Sizcoz method will work better on C3 then
Unfortunately, the sizcoz method is not suitable
The fact is that here, with different text lengths and the same seconds, it works either faster or slower. that is, if the text is different and the seconds are the same, it should reproduce with the same speed of sound but for much longer i.e.
12 characters - 12 times the sound
5 characters - 5 times the sound
and all this at the same speed no matter how many seconds it costs
but in this example from sizcoz he types different tex always with the same duration but either the sound is faster or slower