I'm wondering whether the ship timer on the item page isn't quite accurate, and the one on the checkout goes through and does a warehouse-by-warehouse check to see where the nearest warehouse that has stock and also isn't closed is. As east-coast warehouses close you might get additional availability windows from west-coast warehouses, and their algorithm might not be doing an exhaustive search of when the last possible warehouse that has stock will close.

I'm not saying that it isn't a dark pattern, but there are still some "incompetence" explanations before we need to jump to "malice".

When an organization grows large, the distinction between deliberate malice and beneficial incompetence becomes less meaningful. Inferring an organizations broader culture can be informative, but the net incentives are the same.

It definitely did not feel like a data consistency issue. And the "dynamic pricing" is obviously malicious, but it's the sort of machine-vs-human maliciousness we've been groomed to accept as "the free market".

I don't have a particular grudge, and buy from them if they're the lowest bidder. I just don't understand what appears to be single-minded affinity for them.

That could be a reaction to facts on the ground. To give you a guaranteed shipping window, they need to estimate sales. If sales come up lower than expected, the cutoff moves a few hours.

You see this kind of thing all the time in airline seat pricing.

It's impossible to build a distributed system that has fully consistent results. That is usually the reason for inconsistencies between the detail page and checkout page promises.

The only "distributed system" in question is Amazon's own computer system. In which case no, it does not really seem that difficult to distribute a basically static scalar field.

Your reply seems to suggest that you can get a truck to carry infinite capacity just by using more fuel. Not sure if you meant something else.

This isn't the Internet where links have a bounded capacity and zero marginal cost. The trucks/planes have their schedule - more packages mean more fuel is used, not exhaustion of discrete slots. Delivery services do not make money by queuing packages.

If Amazon had asked for a single truck from UPS at 5 PM from warehouse A (the number of trucks ordered is a business decision), it can only allocate x kgs of packages or y liters of volume to that resource.

Edit: Just to clarify, the number of trucks may often be decided waaay in advance.

The cutoff windows they do give are too long to support your theory (what if demand then spikes?), unless Amazon also retracts those windows (which would also be customer hostile). I'm not saying the constraints you describe are impossible, just highly unlikely based on how every other merchant/shipper works. The tiny gain from optimally packing trucks does not seem to outweigh the additional complexity required to do so.