Elevators

I was finished my work nearly and got ready to go home. However, we are not allowed to leave the office before the end of working hours. The office building only has two elevators, once they do down, it takes a while to come back up to our office floor. That’s why the moment the clock strikes six, several people including me rush to the elevators. Today, I rushed to the elevator as usual. To my surprise, two of my co-workers were already at the elevator hall. They insisted that they left the office after 6:00, I am sure that they left the office a few seconds early.