If you are applying for a job with my company, I schedule an job interview with you at 10:30 and then you show up 30 minutes early at 10:00, that pisses me off. It pisses me off worse than if you showed up 10 minutes late.
When I schedule an interview I pick a time that works for me, so if you show up 30 or 45 minutes early, I don’t see that as “I’m on time and even 30 minutes early! I’m a great candidate!”. I see that as being inconsiderate of my time. So since you decided to show up early, I now have two choices: 1) rearrange what I had planned and see you early or 2) leave you hanging around waiting. Since my office is very small and the only place to wait is right in the middle of the busiest work area, if I make you wait, I now bother all my other co-workers, because they are distracted and uncomfortable with you just twiddling your thumbs in the middle of their workspace.
So don’t show up any more than 5-10 minutes early. Otherwise I might send you off and tell to come back at our scheduled time. And that’s not a good way to start things.