What is a "dust minute"?

A "dust minute" is an extra minute between cars where one hopes that the dust blows away. At a very dry rally with heavy forests and no wind, the dust from the car in front of you may still be hanging in the air when you are driving down the stage. The visibility can be zero. So if the organizers "add a dust minute" it means that they are switching from the normal one minute interval to a two minute interval between cars.