It’s even better with Amazon Prime! If you have an item that does not arrive in the quoted delivery window (you have to be watchful at the checkout screen as not every item will arrive in 2 days even with Amazon Prime) Amazon will reward you an extra month of Amazon Prime. It is not automatic and you have to ask for it. I’ve done this myself twice in the last year and received an extra 60 days before my Amazon Prime membership renewed. How do you go about this?
You can check out the page below and I suggest bookmarking it. Then when you need it, all the info is there and all you have to do is live chat. Be sure to have your order number handy. YMMV with this as some members have reported they were offered a $5 credit to their account rather than the free extra month of Amazon Prime.