According to Amazon, up to three million items marked "Today by" can be ordered for speedy same-day delivery in those cities. Amazon will even deliver packages while you sleep. If you select the "Overnight by 8AM," your order will arrive between 4:30AM and 8AM.

The orders will ship from local fulfillment centers. So, Amazon says, "while it may seem counterintuitive, the faster delivery speeds enabled by these facilities actually help us lower carbon emissions." Because the facilities are close to customers, the quick deliveries reduce the need for aircraft transport and decrease the distance drivers have to travel, the company says. Last year, Amazon pledged to make half of its deliveries carbon-neutral by 2030.

Whether or not these even-faster same-day deliveries are actually good for the environment, or for the people shipping and delivering the packages, is debatable. These mini-warehouses need power, heating and cooling, all of which lead to more emissions. This model could also encourage consumers to place more frequent, smaller orders, resulting in more trips, and again, more emissions.

While the local warehouses will create more jobs, Amazon doesn't have a great employee-satisfaction track record. It may get even worse if Amazon starts asking more employees to work overnight and deliver packages at 4:30AM.