I am guessing under $35, you now get charged for one day.
But this just changed within the last EDIT: two days.
It used to be FREE even under $35.
Same-Day Delivery Rates
Same-Day Delivery is available for customers shipping to select zip codes. Same-Day Delivery rates differ for Prime members and non-Prime customers.
If you’re a non-Prime customer, we’ll calculate your total shipping cost by adding the “Per Shipment” cost and the “Per Item” cost.
Order Type Same-Day Delivery Cost
Prime customers – Eligible orders over $35
Prime customers – Orders under $35
Up to $2.99 per shipment
Excludes Amazon Gift Cards. Amazon Gift Card shipping is free.
h/t KETCHUP PACK SHORTAGE!