Then, the speed when coming back becomes: 80 * (1+0.2) = 96 km/h.
Time used: 20/96=5/24 hours.
So it takes less time to return than to go: 0.25-5/24 hours.
That is, (0.25-5/24) * 60 =15-12.5 = 2.5 (minutes).