I can't tell you what UPS does 'cause I never worked there but I did work at FedEx and...
It makes no difference if you pay extra for guaranteed morning delivery. The package will be delivered in the morning if the truck gets there in the morning as it runs its regular route. But, if that stop is on the truck's afternoon route, then the package will arrive in the afternoon. There is no special "morning delivery" truck. Few people follow up and file a claim if the package doesn't make it at the promised time...but still makes it that day...and FedEx makes muchos extra money.
At least this was the way it was ten years ago.
We've had a morning and separate afternoon FedEx guy (well two guys) at every company I've ever worked at in the city.
Morning guy brought the 10:30 AM stuff around 9, afternoon guy everything else. Same deal with UPS. Either would take outbound packages. This is at work.
Now...
Moving to the country, your scenario is common at home, and what the local store owner also reports. Stuff sometimes comes by 10:30 but more often than not, the afternoon guy just shows up a little earlier around noon.
Not too many folks care much about the extra hour and a half. He delivers the early stuff first and then drives around doing the late stuff unless he sees an opportunity to drop next door to an early delivery.
FedEx Ground on the other hand, rarely shows up to the neighborhood before 5PM, which this time of year means they're running around on frozen dirt roads in the dark. Totally different setup there. Trying to deliver residential stuff after people are home from work.
UPS consistently shows to the front of the 'hood two miles away around 1PM, which puts him in my driveway about 2PM. He's a funny guy, long haired, looks like a throwback to 1975, and wears shorts even when it's 0F out. Totally nice guy but can't stick around long. He's always in a hurry but not rushed.
Can whip that brown truck around in my driveway faster than I can point out to him that it's a circle and he's welcome to just go around the circle so he doesn't have to do anything but jump out as he comes to the mud room door. The circle has some grass growing in the gravel so it kinda doesn't look like it's part of the driveway. Needs to be sprayed and killed this Spring.
She also lives in the 'hood and knows mostly everyone. She's been rumbling about retiring, which will suck. We'll all have to adjust to the new carrier's ways. Maybe she'll hold off a while on retirement. She has a fill in lady on her days off. Maybe the other lady will take over. Dunno how the pecking order works for that. 
