DCL recommends noon or later for flights.
we have had them as early as 11 and made it ok but if there were any delays at all we would have missed our flight.
Its about 45 minutes from the port to OIA, with no delays. So figure an hour to be safe.
The way the road is set up there are very few pull offs so if someone blocks the road with an accident you will NOT be able to get around. So allow plenty of time. we had to wait one time for over an hour on our way to the port.