The dust will last for 6 months to a year. One pound of dust will cover 1,000 sq. I have a few questions regarding carpenter ants. I believe we have a nest inside the house in the basement. The basement is not finished.
Carpenter ants can and do nest in insulation.
You may have to pull out the insulation to find them. I would try spraying the entire perimeter with Demon WP or Suspend . We have a small problem in our vegetable garden. We have little red ants by the thousands. They have eaten the tops of the carrots, but have done nothing else.