If you work Mon to Fri, that's 10 hours a day! I can't see something like that becoming best practice. I think it's naive because PhDs don't work like that. Factor in that most PhD students (me excluded) have lives, families and part time jobs, it's ridiculous. Personally, I don't see how they could ever enforce something like that. As we know, we all move at different rates during different parts of our PhD.