I agree with your 80/20 prinicpal. However, I don't believe that staying late at the office is any indicator of productivity. In fact, I would argue that staying late at the office may have the opposite connotation.

Sure, staying late makes sense sometimes(deadlines to meet, production bugs, making a client happy, etc), however, staying late on a regular basis would indicate to me that these people are either very inefficient, need some extra manpower, or have a process problem.

Hours worked does not equate directly to productivity.I think believing that they do is a toxic mindset.