You’re Not Early Enough
Remember, folks, it’s not your job to do your employers any favors. They’re paying you to work from 9 to 5 or, in this person’s case, 10 to 7. However, out of the goodness of their heart, the OP decided to come into the restaurant early in order to help in any way they could before the restaurant officially opened.
So, one day, the OP came into the restaurant at 9:30, which was half an hour before their schedule, but that wasn’t good enough for the employer. Due to their tardiness for being early, the OP found themselves out of a job.