Funny, it seems it took less than a year to bring EV cars factories on line. For a product NO ONE WANTS....
Existing plants and production lines can be repurposed more quickly, but building large new plants on green fields takes longer, to plan and build out water, sewer, power, roads and rail; as well as the actual plant and equipment.
Some manufacturing equipment itself has a multi-year lead time time to procure. In some areas, plans include establishing skills training programs with local Governments (like Community Colleges) years before start up, to prepare an adequate workforce.
We are talking about significantly expanding the total US manufacturing capacity, with all new, as well as expanded, facilities and workforce.
In particular, Texas has been a winner in attracting new plants.