"How man years" = DEPENDS. Depends on a number of factors. I think you can start forming strong opinions early on, but usually need to give some time.
In the case of Pitino...
That's from this preseason article. The Gophers - as of today - project down next season. But.. you need to look at not only what the team does this year and next (including looking at the newcomers that are brought in for 2015), but also where he stands with key recruits for 2016 and beyond.
Next year could be rough, but with help on the way. That may mean 2016-17 doesn't project all that well, but the following year does.. all just depends. From a PR standpoint (which is largely mindless crap that a non-thinking fan can grasp onto), this season would be nice to earn an NCAA tourney berth... because the risk he runs is not getting in this year and then having a rough year next season... puts him in a less favorable light (right or wrong -- wrong, mostly) a year and a half from now.
Time will tell. He has a lot to prove, but the ceiling for the program is gigantic in comparison to what it was with Tubby here in his last couple of years.
Texas Tech now 10-3! Oh, how they will crumble. AWFUL.