What happened here wasn't that the copilot sat there waiting for the intended time to come about and pressed the button exactly at that intended time and just didn't know what the time was supposed to be. What happened was that he was frantically trying to concentrate on a zillion things at once and pressed the button a bit early because he thought otherwise he might end up pressing it too late and he had been warned about the dangers of pressing it too late but not about the dangers of pressing it too early. If there had been an autopilot, most likely the autopilot would have pressed the button at the right time while he was looking at something else.