I think he's doing a perfectly fine job thus far. He inherited a mess of a football club and has built it up well. So much so that in the space of two and a bit years we've gone from Smalling and Sanchez to Varane and Sancho.
At the outset, he's had a plan and he has diligently stuck to it, even being patient and not settling for 2nd or 3rd choice options, etc. Yet despite how slow and anemic our board has been in getting the necessary deals over the line, he's still managed to improve us and the players that were already here. Some of whom were borderline jokes.
So I'll say this: your asking how much time does he need, hasn't he done enough so far in his time here, with a largely inferior squad for most of it, to be given that time? Even now, this board hasn't gone far enough in its support of Ole to give him the DM that he badly needs to assure us of a title challenge. As soon as I can say that he has the tools necessary to succeed or fail, then I will be willing to give him the time and benefit of the doubt. If he drops out of the top 4 however, then he'll have to be let go as that is the bare minimum. I'm expecting more as Varane and Sancho will naturally elevate us above the top 4 challengers like Leicester, but as far as the board is concerned, top 4 is that threshold for them