@ken most work has downtime, even a computer can go idle every now and then waiting for something. The work hours are about dedication, in that time your work is your top priority, you must be active as soon as it's possible, as much as it's possible, constantly fussing about improving efficiency of the process, you must be available for your co-workers or clients if they need you and accountable for a certain portion of the work. In other words if there is nothing to do you must think of something to do and you must always be ready to go. That's the idea, not constant uninterrupted mechanical work, it's a form and a measure of dedication.

It's actually much easier to be flexible if the work is very mechanical and definite. Like if your job is to build some ginormous lego set by end of the week then nobody would care when and how you do it as long as you do it in time.