Might be item dependant, I recently ordered something on Saturday afternoon and it was delivered by 11am Sunday
It will be this. I live near one of the biggest fulfilment centres so almost everything arrives next day and a lot of have the option for within two hours, but I ordered something quite obscure the other day and it was two days, even though prime.
I fucking love amazon prime, their TV package is great (just got every seinfeld in) and I read kindle books so I get loads of credits when I do that 'no rush' bonus thingy.