Where would be the best place in time for the CP to win WWI, "best" meaning with least likelihood of revanche downstream: if the Germans were to win a conclusive victory, nullify all chances of French angst leading to a new war (as did the Franco-Prussian War), leave the Russians so lean as to be unable to contemplate war on any European front, astound their own allies into perpetual cooperation (Italy included?), and most of all leave the British glad to be out or glad never to have gotten in, where would that time be?
I don't think a victory on the Marne would do. Perhaps if the Germans pulled back all but a skeleton crew from the western front and bled the allies dry fighting for stale inches of non-German ground while attacking ferociously on the eastern front the CP might have won by destroying the weakest link. Russia would thereafter retreat upon herself while in the west Britain and France would be dubious allies of necessity, perhaps willing to concede the fight if Germany withdrew to her own borders by mid-1915.
But what are your thoughts?