In both Oakland and Colorado, I have also seen very poor rates of successful 2-day Prime delivery. Often indeed, the item ships about 5 minutes before the "Item will arrive by 8pm today" commitment (and that message will continue to show well after 8pm and the item has not arrived).

I order things like food from Amazon (Soylent), and I have relied on the shipping. But it is awful. I would say about 50% of the time my package arrives late, by a day or even 3-4 days. It's insane to pay $100 a year for a service that absolutely does not meet its promises. Just call it 4 day delivery and we'll be good.

Amazon Prime is a scam. I'm a loyal customer because there are few alternatives, but they do not deliver the service that you pay for.