Here in my area, 2-day Prime means 3-4 days. Their guaranteed delivery date is always 4 days away, but about half the time you'll get it in 3. But they still call it "two-day delivery"
I think it now means two days from when they hand it off to usps/ups/fedex. There has been considerable delay recently from when the package is "shipped" and when it's handed over. Probably due to them using their own trucks and simply using the other carriers as the last mile.