If you get paid by the hour, sure. But if you are salary, you are reducing your hourly rate by doing this. That means you are cheapening the value of your own t

If you get paid by the hour, sure. But if you are salary, you are reducing your hourly rate by doing this. That means you are cheapening the value of your own time. And you are screwing your co-workers. There is nothing wrong with getting into the flow and working a few hours late. Just tell your boss and leave early on Friday. Even if leaving early means coding on your side project.