UPS & FedEx guarantee each package to arrive by a certain time or it’s free.
The late delivery refund policy can be summarized easily: assuming there are no exceptions (weather delays, address correction, customs delays, etc.) your package is guaranteed to arrive on time or you as the shipper are owed a refund- even if that package is one minute late.
As the shipper, you have a 15-day window to claim these late packages.