a postman has a round that'll start in one street, say 8am, then continue with streets in a set order. The reason u get mail at 11am is simply because your street will be one of the last on the round. You don't get 1 postman for each street!

Agree about the wrongly delivered mail, happens atleast once a week where we'll get mail addressed to someone with a similar street name to mine. That's sloppy.