It is rude to not arrive on time.
Mary needs a job and her friend got her an interview at her place of work.
Mary wants to go to the interview.
Mary gets to the job interview early in order to make a good impression.
Mary gets to the interview over twenty minutes later than it was scheduled.
The interviewer is impressed by Mary's punctuality and gives Mary the job on the spot.
The interviewer dismisses Mary, and she doesn't get the job that she wanted.