6 months is arbitrary. The areas in which he needs to improve are not system related.I have very clearly said Havertz needs at least 6 months to properly judge him, while all players coming from other leagues should get at least 12 months. Take note of the word properly.
This is because Havertz is learning back to midfield position, which is also different than the AMF position he played at Leverkusen years back, because it's Arteta's LCM role. Not coming to a new league, so he is already adjusted in that sense. So 6 months looks like okay time frame.
I think it's very fair to give him more than a few games before proclaiming he is a flop or something. It's not that hard to understand how much different it's to play striker in horrible Chelsea tactics last year vs. LCM in Arteta's tactics.
Why compare to Quaresma, who is also a winger? His problems were not similar as Havertz, who mostly has confidence problems as far as I know?
And there you go, ending it as knowing it was a **** transfer already. There was no one else with a similar profile on the market who was EPL proven/adjusted. Arteta wanted a target man, and likely wants another to the striker role in the future.