Cold-chain box ship windows, how do M/T/W cutoff rules work?

Three coupled rules:

• Ship-day-by-zip table, a Magento custom table mapping every ZIP (or postal code) to the carrier (UPS Ground / FedEx Ground / OnTrac / regional LTL), the transit-day count, and therefore the ship day that lands the box on the customer’s chosen delivery day. East-coast zips ship Monday for Wednesday delivery; west-coast zips ship Tuesday for Friday or Saturday delivery.
• Ice-pack count by ambient temperature, daily cron pulls a 7-day weather forecast per fulfillment warehouse via OpenWeatherMap or Tomorrow.io. Box composition rules: 2 ice packs at <60°F ambient, 3 packs at 60-80°F, 4 packs + insulated liner upgrade at >80°F. Pushed to the 3PL kitting system as box-composition metadata on each order.
• Carrier mix, UPS Ground for 65% of US zips, FedEx Ground for 30%, regional LTLs (LSO, OnTrac) for high-density zones with same-day pickup. Shippo or EasyPost for label generation. ShipBob, Ryder, or Misfits Logistics for the cold-chain 3PL itself.

Saturday delivery available on Mon-ship for west-coast zips. Sunday delivery is rare, carrier capacity gaps; only Sprouts and some Amazon Fresh routes do it cleanly.