We have absolutely no idea when Bayern first made contact with Juventus over Vidal if we're being honest. There's no way of knowing. They could, just as easily, have discussed the deal with Juventus and Vidal prior to the Copa America, which would put it at well over a month. Technically City haven't made contact with Wolfsburg, officially, at all at this point so, technically, the clock hasn't started on this deal, it's really just paper talk at this stage. Obviously, in reality, everyone knows what's happening, but maybe Bayern and Juventus, in the case of Vidal, were happier for this not to be played out in the public eye. Wolfsburg need to be seen to be resisting before they sell for what needs to be seen as a "price they couldn't turn down", the same is true of the Pogba deal for City. Vidal, on the other hand, had been at Juventus for 4 years and Juve were happy to sell, hence that deal (on the face of it in any case) looking easier, and quicker, to complete.
Sometimes deals can be conducted very quickly indeed, but in the vast majority of cases, certainly when you're talking about the financial commitments City are looking to make, these things can be very complex, and complex deals take time to finalise.
