Delivery timeframes are estimated and displayed accurately

Customers who cannot see when their order will arrive either abandon checkout or open support tickets after purchase, both of which erode margin. Delivery-date visibility is a core commerce UX expectation set by Amazon and reinforced across every major retailer; its absence signals an amateur storefront. Gift buyers, event buyers, and deadline-driven purchases all require a concrete arrival window to convert. Missing or identical timeframes across methods also defeats the purpose of offering tiered shipping in the first place.

Compute a delivery estimate per shipping method from processing days plus transit days, skip weekends (and optionally holidays) during the walk, and render the resulting date or day range next to each method label in the checkout selector. Centralize the logic in lib/shipping.ts so order confirmation emails and product pages can reuse it:

export function estimateDelivery(method, orderedAt = new Date()) {
  // walk business days: processingDays + method.transitDays
}