The "free two day shipping" I get from Prime is "two day by 8PM". Do you know your mailman delivers as late as 8PM? I know they don't here, and neither does UPS or FedEx.
As I understand it, you'll get packages at 8 if you're near a depot, if you're in a city with lots of businesses, or if your calendar says "December".
Even in your area, they probably deliver things late around the holidays. There's a period around Christmas where the package delivery services hire lots of extra temp employees to handle the extra load, and the delivery hours tend to get extended as a result. I think I even remember seeing one of the carriers in my neighborhood after 8 on occasion.
Also, if you're close to a FedEx or UPS depot, they'll do runs even later. Their depots are both within half a mile of the edge of my neighborhood, so every FedEx and UPS truck in the South Bay literally comes around the back side of my neighborhood when they get off the freeway an exit early to avoid the last two miles of parking lot on the 101.
As a result, I routinely see FedEx and UPS out at six or seven at night making their rounds as they work their way back to the depot at the end of the day, and I've seen multiple trucks doing deliveries here—presumably because they know that they can just toss our packages onto pretty much any truck that goes out that day, and it will be close enough to their route to not be a problem. :-)
Finally, if you have a lot of businesses nearby, they'll deliver your packages after hours. They have to get all of their business deliveries finished by 5:00 (or maybe 4:00, I forget), which means that home deliveries usually happen either early in the morning or in the evening.
As always, YMMV.