Glen Mason was by most accounts an above average coach At-BEST. He was an overtime loss to Wisconsin away from winning the Big Ten in just his third season in Minnesota. Glen Mason was taking over for Jim Wacker who had been the coach in what was the worst period of gopher football history. He was doing it with Wackers players and running a different system and he turned it around in just 3 years.
It doesn't take 5-10 years to rebuild. It takes 5-10 years to build into a consistent winner year in and year out. People have vastly overinflated the period of time in which it takes to get a program back to a competitive level.