Taken from the Ship You Reptiles FAQ's:
For most addresses, your Priority Overnight package will arrive by 10:30 a.m. Tuesday through Friday.
Note: In some outlying areas, Priority Overnight packages are delivered by noon. In farther outlying areas, Priority Overnight packages are delivered by the end of the day.
To check the expected or guaranteed delivery time for your destination, go to the FedEx Rates & Transit Tool and enter the Ship From and Ship To ZIP codes, choose a shipping date, enter a package weight then click on the “Get quick quote” button.The tracking is just saying it is scheduled to be delivered by 4:30 pm. After that it is considered late.Guaranteed delivery times for Priority Overnight are determined by a three-tiered system established by FedEx. Zip codes that are categorized by FedEx as urban, rural or remote will receive deliveries by 10:30 a.m., noon or 4:30 p.m. respectively. Check the expected delivery time for your destination at FedEx Get Rates and Transit Times.