I ordered two items to be delivered to a building which is staffed 24 hours a day, the driver claimed not to be able to deliver them so I complained to Amazon who told me this:
"As our carriers deliver a large number of orders in a geographical pattern, in most cases, the carrier might not be able to deliver the order on the same day of delivery attempt and it seems that the carrier was not able to deliver this order by yesterday.
Due to this, they have delivered this order today with high priority."
In other words, the delivery on the same day or next day with Prime means nothing if they have given their drivers too much work.