The fine print has always been that it's 2 days from Amazon's ship date and not from your order date.
Even so, they regularly fail on even delivering two days after shipping, and even more often on one-day.
https://www.amazon.com/gp/help/customer/display.html?nodeId=...
Amazon could easily make the case that even though the item you ordered was "in stock," it was still unavailable to ship immediately due to warehouse backlog or other operational reasons.