A plane travels from Calgary, AB to Grande Prairie, AB. The total flight time, including takeoff and landing, is \(1\) hour and \(40\) minutes. The return flight takes the same route and time. The average speed for these two flights is \(500\) km/h.
After a brief layover in Grande Prairie, the average speed of this entire round trip (including the two flights and the layover in between) becomes \(425\) km/h. How long was the layover?