What laying down six Yorktowns in 1939 would change

How many additional Yorktown-class carriers could be laid down with Hornet, and how would they affect the war?

Perhaps five more, producing earlier multi-carrier operations but also foreign responses and a larger escort requirement.

Five additional American yards may have been able to lay down Yorktown-class ships alongside Hornet in September 1939. Because Hornet commissioned in October 1941, parallel construction could put several more carriers into service near the start of the Pacific War. Those ships would enable more multi-carrier raids, but they would also require additional escorts and supporting vessels. Japan and other powers would respond to such an obvious break from treaty restraint, so the scenario cannot be evaluated as a one-sided American expansion.