You don’t have a backup portal?!?

You didn’t bang on the door of the post office and demand they ship your package RIGHT NOW?!

Just curious, what did you reply?

I wonder if the customer is just this incredibly impatient, or if they sent their message to the wrong seller and they have a different item that is late?

It’s a drop shipper I would bet

You haven’t invested in Amazon’s drone delivery yet?

Even if you could instantly transport the item to the customer, you would still have a problem, How would you prove delivery!!!

Did the order by any chance come from George or Jane Jetson?

Neither am I in these cases.

I normally wait to respond to the buyer and remind them they placed an order on the weekend and the message they sent about the order being late was sent one day after ordering. I’ll then apologize they believe the order is late, remind them of the max delivery date then cancel their order. In some cases I’ll first increase my handling time substantially just in case they re-order and will drag my feet on shipping the item. If it were eBay, I’d also ban their user name as I have no desire to deal with buyers like this which are unfortunately commonplace here on Amazon.

Amazon is spoiling bad buyers at sellers cost.
Most of the time buyers think they buy from the big giant and rich Amazon, not sellers. So they act like a spoiled child and if you don’t do what they want they have the powerful bad review gun and you have no defense.
A few days ago I had a return for the reason “arrived too late”. The order was placed Feb 18, 7:26 PM. Delivery by: Tue, Feb 23 to Fri, Feb 26. Item was shipped next day and arrive on Feb 22, exactly one day before the first expected delivery date.
Meanwhile our money goes to USPS to take our products for a short round trip.

Trust me - people are highly over-rated.