"Mr. Cook closed Apple’s factories and outsourced all manufacturing to a far-flung network of suppliers in Asia. Inventories decreased to 60 days, then to 30 days, then to the just-in-time model. Mr. Cook virtually lived in airplanes, traveling the world to meet with suppliers and browbeat them into meeting his demands." http://www.nytimes.com/2011/01/24/technology/24cook.html?pag...

I can't say how long it takes to make every part, but it seems like Apple has leverage with its suppliers. I do agree that looking at the 5 day metric is only part of a picture.