Recently, we have witnessed candidates arriving 40-50 minutes for an interview and having to endure a long wait in the reception area before being called in for their interview. Some have even met their interviewers setting up the interview room prior to their interview. Your interviewer is not only thrown off kilter by your early arrival, but may be annoyed by your presence.
Even if you do not meet your interviewer, you may be a source of annoyance to the receptionist, who may feel compelled to engage a small talk with you rather than focussing on his/her workload.
How early is too early?
I would consider anything over 20 minutes too early. The ideal time to arrive is 15 minutes before your interview. This will allow you plenty of time to compose your thoughts and familiarise yourself with your new surroundings without becoming a source of annoyance. If you arrive at your destination too early, wait in the car or take a quick walk around the block so you can time your entry into the building 15 minutes prior to your allocated interview time. Otherwise, your eagerness could have a detrimental effect on your interview outcome.