I agree it is quite likely also a scheduling challenge. But it doesn't matter how difficult it is to compute, my take is, that there is so much variation in the

I agree it is quite likely also a scheduling challenge. But it doesn't matter how difficult it is to compute, my take is, that there is so much variation in the intermediate steps which have a mutual dependency, that an elaborate schedule wouldn't last for long. Like a truck with sand arriving a few minutes early or late to the site. So the construction workers will dynamically have to deal with the situation. And at times step aside and wait for that truck with the sand dump it into the pit they are working in. And of course, beyond what was said about the workers needs for breaks, it might be most efficient to have reasonably large groups of workers which are needed to work together to perform a task efficiently and then that group having short breaks between the tasks instead of trying to have schemes how to increase the utilization per worker.