It is paramount. This way I can leave 4:30pm (or earlier) minimizing the perception that I might be slacking off (which I am not). Other guys that get here after me stick around way past 6pm, which for me is a no-no. Since no one has any idea what time I came in, it gets harder to judge. I wish this was not necessary but it is my defense against company culture (8 solid hours, no working from home, regardless of your current work load).