Why should he stay later than that?

I've never understood offices where employees stay late on purpose to prove to their bosses they're dedicated. If anything, I think staying late at work shows your boss you're bad at time management, but not everyone agrees with me. A lot of bosses want their employees to stay past the time when their workday ends, and the boss in this story is one of them. She thinks her employee's clock is off, but doesn't get why he doesn't think leaving a couple of minutes early is worth commenting on.