In almost all the talks I have physically attended, running overtime I observed is closely correlated to how visibly the audience start showing signs of tiredne

In almost all the talks I have physically attended, running overtime I observed is closely correlated to how visibly the audience start showing signs of tiredness no matter what the topic is. I feel like it is not about 52.x minutes, it is more about expectations. If the talk is 20 minutes the audience expects it to be over by 20 minutes.