Before the customer asks “when?”
A delivery date is part of the product decision.
Shoppers rarely think in “two business days of processing plus three to five in transit.” They want to know whether the parcel should arrive before a birthday, a trip, or next weekend.
If that answer is missing, the customer either asks support, postpones the purchase, or makes an optimistic guess that becomes your problem later. A useful estimate moves the calculation onto the product page, while there is still time to set the right expectation.
The estimate has to be believable.
A date that ignores weekends, warehouse cutoffs, or a holiday is worse than no date: it creates a promise the operations team never made. Start with the simplest rule that reflects how the store actually fulfills an order.
Build the baseline from work your team really does
I would resist the urge to begin with every exception. Enter the normal processing window, transit window, and working days first. Add the daily cutoff so an order placed late in the day does not appear to start moving immediately. The app combines those inputs into a customer-facing range and uses the visitor's locale and date format automatically.
