80 kt in 20 s is an average acceleration of 2.06 m/s2 or 0.21 g (with no wind) and the distance rolled ~= 1350 ft.
With the same constant acceleration of 0.21g, 150 kt would be attained in 37.5 s for a rolled distance of 4750 ft or 1450 m (still with no wind).
This 20 s limit looks a bit too conservative.