Amazon ships about 3,300,000 boxes per day. Your order will be shipped in the order in which it's received(depending on how it fits efficiently into the pick/ship system), however Amazon has made a contract/commitment to the Prime members which must be honored first.
In other words, back of the bus, boy.
I don't do a lot of shopping, but much of what I do buy comes from/through Amazon. Even so, I've avoided Prime because it annoys me about as much as Disney World's system of if you pay more you can skip to the head of the line. Capitalism was never meant to be fair. sigh