It might be OK in the company policy, but where it counts is co-worker and manager opinion. I personally have found that coming into work at 7am and working til 4pm just doesn't fly with other co-workers. They get the opinion that I didn't have to work as much as everyone else. Productivity can be hard to judge, so it's easy to revert back to time in the office.

I believe there was a study at Google that had similar results as what I experienced as well.