I don't know if this has been mentioned before but i have several books on the Soviet invasion and the disaster of Hitlers meddling in the invasion, even before the beginning Hitler meddled in the Soviet invasion

Hitler ordered in June 1940 that plans be drawn up for the eventual invasion of the Soviet Union, so the Chef der Stab of the German 18th Army a Generalmajor Erich Marckes was chosen to draw up plans for the invasion of the Soviet Union and after sometime Generalmajor Erich Marckes drew up his invasion plans and they were to be.

The main thrust was to be towards Moscow, while smaller spearheads would target Leningrad and Stalingrad, and the eventual result would be the securing of the A-A line, the invasion would take place sometime in late April or early May, time for the invasion was to take 12 weeks.

But here was Hitler and his meddling began, while Generalmajor Erich Marckes was prepareing his plans, Hitler ordered Keitel and Jodl to prepare shadow plans specifically to target Stalingrad and Leningrad, Moscow was of little importance, so the OKW began to prepare their shodow plans. To begin at more or less at the same time.

Hitler as he was chose the shadow plans an went with them. But fate stepped in and dealt the Third Reich a blow, and that was the Italian debarkle in the Balkans/Aegean, that delay cost the Germans dearly.

So had Hitler decided that the Italians had to handle the Balkan situation by themselves and not diverted his forces and used Generalmajor Erich Marckes plans i would say that German/Axis forces could have secured the A-A line by at least by September 1941, that includes the capture of Stalingrad, Leningrad and Moscow and the Caucasus Oilfields by December and then defensively weathered the winter and the following spring/summer launch another offensive to the Urals by December 1942.