They usually start very early in the south - Ocracoke Is, Frisco, Avon and then work their way up the banks. My bet Duck will be a early Thursday evacuation if the storm stays on track. If Arthur goes out to sea just a little more they are far enough north that they may be able to stay. While those in the south will definitely be evacuated.
We had a place in Waves many moons ago and were forced to leave about 36 hours before the storm. Had to exit via 64 the Manteo bridge, while the folks up North (Corolla, Duck, Southern Shore and Kitty Hawk had to leave via 158 through Currituck.
Anyway you look at it the traffic SUCKS when everybody leaves the Outer Banks in a hurry and upset their vacation ended early. Hope the best for your friends.
-------------------- “Though we travel the world over to find the beautiful, we must carry it with us or we find it not.” - Emerson