>...although I didn't find anything over 30 days, FWIW.
Because on the seller's page when data-entering the product's details, the maximum value allowed is "30 days". Princeton Audio wants "42 days".
Also, none of your examples have the valuable imprimatur: "Ships from and sold by Amazon.com."
PA wants a combination of "audience reach" + "flexible logistics" that Amazon doesn't currently offer.
I'm no Amazon Homemade expert, but there are plenty of items that say they take time to make:
* Usually takes between 21 and 30 days to create
https://www.amazon.com/Live-Edge-Dining-Conference-Table/dp/...
* Usually takes between 21 and 30 days to create
https://www.amazon.com/Omondi-Odhuno-Originals-Traditional-M...
* Usually takes between 21 and 30 days to create
https://www.amazon.com/Heroic-Bronze-Sculpture-Statue-Fraser...
* Usually takes between 21 and 30 days to create
https://www.amazon.com/Abstract-Metal-Sculpture-Aircraft-Alu...
* Usually takes between 21 and 30 days to create
https://www.amazon.com/Stained-Glass-Window-Herons-sunset/dp...
...although I didn't find anything over 30 days, FWIW.