"They" being the people in charge, not some random "longtime employee."
What I mean is, either you watch the clock or you don't. If you watch the clock, you come in at x:00 am, and you leave at y:00 pm. If you don't watch the clock, you come in by some reasonable time, stay 'til your work is done and leave. If your work isn't done 'til late, you stay late. But if your work is done early, you leave early. It's not reasonable to say you work "at least from x to y, unless there's more work, then you stay late."
Pick one and live with it.
IMO