It's all about timing!

Show up early, you're over eager, show up late, you're done. Give yourself PLENTY of time to arrive at the interview at least 10 minutes early. If you find yourself 15+ minutes early, then stay in your car, hang out in the lobby of the building, or really do just about anything other than walk into the office so early as to make them see you as desperate.

Late does not work, and on the off chance that you show up late, it better not be more than a few minutes, and you better repeatedly apologize and have a good reason.

Great companies want to hire great people, and they will be quick to find fault. There are things that are beyond the control of the candidate, timing is not one of them. Always maximize the opportunity. Be five to ten minutes early and send a signal to the company that you're meeting with that you value the opportunity and respect their time.