The Delivery Rule states that the probability that a delivery person will arrive at the beginning of the delivery window is directly proportionate to your readiness to receive them. It’s compounded by the delivery’s size and complexity. The less ready you are, the more on time, or early, they will be. If you’re in the shower or not dressed at the beginning of the window, they will be at your door.
They don’t want to be, but that’s the rule.