The conventional wisdom says you have to give a coach 4-6 years to bring in his guys, install a new culture, etc. I’d argue signs of significant improvement should be there by year 3 or most coaches will start to have the smell of 3 day old fish to recruits, fans. Historically, I’m not sure any of the really successful coaches have failed to either a) meet the prior coach’s level of success by year 3 b) failed to meet a program-specific level of success or improvement, eg 8-10 wins and signature wins by year 3.
PJ has met the signature win requirement (albeit a slightly “down” Wisconsin squad but who really cares - that in and of itself is exciting), and there are signs of improvement on offense and possibly on defense.
My theory is that it may be better to cut bait with coaches sooner rather than later. Time and again new attitudes, new outlook, new teaching methods can make a difference as we saw with Robb Smith. The counter to that is some coaches will be fearful of going to schools with a quick hook. I doubt that argument, but I suppose it could be a factor. Most up and coming coaches will jump at virtually any P5 job because they are wired to overcome adversity.