According to Slate article, same day delivery.
Original Operations model:
Amazon’s grand strategy has been to set up distribution centers in faraway, low-cost states and then ship stuff to people in more populous, high-cost states. When I order stuff from Amazon, for instance, it gets shipped to California from one of the company’s massive warehouses in Kentucky or Nevada.
Amazon’s new goal is to get stuff to you immediately—as soon as a few hours after you hit Buy.