Timeliness tends to be a big issue when it comes to hiring at my organization. At the special request of a co-worker, I'm dedicating a post to the all important issue of arriving at the appropriate time for interviews.
Obviously, you should do everything in your power to show up on time - preferably about 10-15 minutes early. We often have paperwork that you will need to complete when you arrive, and if you get here early you can get started right away and we can actually start interviewing you at the designated time. However...please do not arrive more than 15 minutes early. When I used to hire for temporary positions, every week candidates would arrive at least AN HOUR EARLY. I'm sorry, that's ridiculous. It makes it look like you have nothing better to do and we feel a bit uncomfortable with you waiting in our office for that long. Even 20 minutes early is a bit much.
Personally, I feel a bit self-conscious when a candidate arrives - I want to make sure we're all on our best behavior around you and that you are greeted and treated well. But I also have work to do and being forced to close my office door so I can make phone calls while you hover in the next room is...well, awkward.
Now, it's fine if you plan ahead and arrive at the PARKING LOT early! In fact, I think you should plan to arrive at your interview location at least 30 minutes early, but wait in your car until 10 minutes before. This will give you a chance to calm your nerves, review your research and jot down potential questions ahead of time.
And obviously...don't be late! Or if you realize you may be late, pull over and call the office immediately to let them know and apologize. If you just show up late, I might not have time to interview you at all...and you've given me a very poor first impression of you. Remember, hiring managers know that the "you" that you present us on the day of the interview is probably the best version of yourself. So if the best version of yourself is late....well, don't count on getting the job.