Will you have checked luggage? That's where you usually get held up - I've had the baggage on the carousel by the time we got to baggage claim or other times waited 20 minutes or more.
Are you renting a car? If you have counter service, you will probably have to wait in line at least 10 or 20 minutes. If you are using Mears, you will have to wait for a van.
Once you are out of the airport, it's usually about 30 minutes.
When I was there in May, everything went perfect. The luggage was coming around when we got to baggage claim, we used Emerald Aisle at National, no traffic on the Greenway. It was about an hour from plane landing to OKW parking lot.