I'm a Prime member. If I order something Monday, I'll sometimes get it Tuesday, but it's usually Wednesday.
The delays often happen, I find, when UPS delivers it to the local post office for the final leg of shipping (I think this is what they call "Smart Post" shipping). A number of times in this type of situation, I check online and they show that the package has been delivered, when in reality it's still on the mail truck and it shows up the next day. It doesn't always happen that way, which makes me think that there's one Post Office employee who's cooking the numbers to makes sure that everything on his truck is shown as "delivered" at the end of his shift.
I actually got an Amazon delivery on a Sunday one time - first time that ever happened. They used a different third-party delivery service that I'd never heard of before. That was weird, because nothing ever gets delivered on a Sunday - except pizza and Chinese food.
