Port arrival time - how strict?

[Raya]

We got a 12:30 Port Arrival time. The car service has told us to expect an 11AM pickup. As nearly as I can tell the Port is only about an hour away from us. What will happen if we arrive 30 minutes early? I'm sure the car service is building in a cushion (we told them our arrival time needed to be 12:30) but I'd hate to start the trip by standing outside in the sun for 30 minutes.