I disagree. If the call sheet says 8 am, that's when they want to start. If you turn up at 8 am then you are not ready to begin. Turn up at 7.45 am and you are. And besides, you don't know what the travel conditions might be like on the way to set. If you have timed your entrance to perfection for the call time and your car won't start then you are going to be late. If you plan to be there a bit early, you give yourself wriggle room.