Is there no type of work a human can do in a short time which has value? Say in 20 seconds. If there is such a task, then it can't be automated. Because then

Is there no type of work a human can do in a short time which has value? Say in 20 seconds. If there is such a task, then it can't be automated. Because then it would not have value. So we could base a captcha on performing that task. If there is no such task - what is the minimum amount of time in which a person can create value? If there is no task for any length of time in which a human can create value - well, then we are all jobless :)