Improvement at the very least. I always feel like after big changes like this summer for example, the more time with those changes should see a positive impact. As long as the positive impact is there overall (runs of form either way is not included in this), then they should stay. Van Gaal was on a positive trend until a few months into the 2nd season, and then it went really badly (after a really poor summer and pretty much all of his signings failing). Mourinho was on a positive trend for 1.5 years, but then from January 2018 onwards it went to shit. Ole took over, had a good instant impact and then the squad tired and couldnt keep it up, and notably the glaring issues in the squad became exposed and are holding us back. You would assume if we fix those issues with his types of players, then we'll improve. If we keep improving then there's no reason to move on from him. Doesn't take too long to spot progress IMO, but you also need a pre season and a summer window to have a chance to put your stamp on the team. Taking over mid season, all you can do is some minor instructions and motivation, no squad overhauls.