The earliest Adolf could have jumped opn Barbarossa was about a week earlier than he did. Turns out the weather had a lot more to do with any delay than Yugoslavia, Greece and Crete. It was a VERY wet Spring, especially in Ukraine, and the Germans had to wait for the ground to dry out sufficiently for operations [remember, the German Army was about 80% to 90% horse drawn, and in 1941, most Grenadiers rode in trucks, not half-tracks.
Where pulling Mussolini’s chestnuts hurt the Germans was in wear and tear on the vehicles used in “25” and “Marita”, and the airborne losses [troops and Ju-52s] in “Mercury”.
As for the problems that arose later in ‘41 for the invasion, blame the split in the German command over how to proceed once Smolensk was taken [Hitler had to referee that one], and Halder and the General Staff’s almost overt refusal, in developing the plan for Barbarosa, to do what Hitler wanted.
Now I do believe in the long-run the Germans were doomed in Russia, but at least I wished they would have had enough success that it would have resulted in the overthrow of Stalin and the Bolsheviks by the Russians.
Hitler and his general staff both miscalculated when they believed they could defeat the USSR in one summer campaign season with the war material on hand. It was physically impossible to accomplish. Barbarossa required at least a two year campaign with the German economy placed on a full war footing, which it was not.
More on this next summer.