Are Delivery Drivers Psychic?

The other day I was stuck inside for god knows how long whilst waiting for those clowns at DHL to deliver a new mobile phone.
You know the drill, you get an e-mail saying that you're package will be delivered on Tuesday, between the hours of 8:30pm and 6:00pm, meaning that you have to be up by 8:30 and wait until 6:00pm in the vain hope that a bright yellow van will pull up outside your front door.
The thing is, you HAVE to stay in the house because if you go out, even for just 2 minutes, you'll return to find a card on your doormat with the words "You wern't in when we called."

How the hell do they do it? Every single time! Yet when you stay in, it's only until 5:59pm that you get a knock at the front door.
Someone needs to look into this. I think that there's much more to DHL drivers than meets the eye.