Well, if [Operation Barbossa] were to be a two-pronged attack, the target cities would likely be Stalingrad, because it was a major industrial center, and Moscow, the capital and "heart" of the Soviet Union.
Hitler might have to postpone the invasions of Yugoslavia and Greece in April 1941, because the invasions postponed [Operation Barbarossa] by six weeks (May 15-June 22, 1941) in OTL, and move on in with [Operation Barbarossa] on the original date: May 15, 1941.
Then Hitler would have to leave Leningrad alone for the time being, and go straight for Moscow or/and Stalingrad. This way, the Germans might capture Stalingrad by July/August and Moscow by perhaps August/September 1941, you think?