I'm guessing that Dan lives in a property with a long drive or is otherwise set back/apart from more easily accessed homes. The mailman may be shaving time off his delivery by bypassing some awkward properties. It's a saturday and he wants an early finish.
Another possibility is that Mon-Fri he has a regular mailman who knows every delivery point but Saturdays are being covered by a stand-in who is not as familiar with the area.
"I ain't no grown-up, I'm a musician, Godammit" - Antoine Batiste