New York (CNN Business) More than a decade ago, Amazon launched its Prime membership service with the promise of free two-day shipping. The unique offer helped attract millions of subscribers, shifted consumer expectations for shopping convenience and forced other large retailers to try to catch up.

Now, Amazon is spending big to cut that shipping window in half.

Amazon announced Thursday that it plans to invest $800 million in the second quarter of 2019 toward making one-day shipping the standard offering of Prime.

"Our goal is to evolve the two-day free shipping program into the one-day free shipping program, and we're making strides on that," Brian Olsavsky, Amazon's CFO, said on a conference call with analysts Thursday after the company reported record quarterly earnings . "We feel like we are doing something very important for the customer."

Olsavsky didn't specify when this option would be standard for all Prime customers, but he said Amazon expects to "make steady progress quickly and through the year."

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