Please check your tracking and see if it actually says delivered to the final destination. If not, most likely, your package was shipped via UPS Innovation/Surepost where UPS delivers to your local post office for the final delivery. Our system automatically sends you the delivery message when the carrier marks it as delivered. The carrier probably marked it as delivered when it arrived at your post office and triggered the message. It will likely be delivered the next day or so.
Also, some packages just may show up next day show up the next day for some reason. Strange, but it happens!