I'm tracking an enevelope sent via the USPS with priority mail tracking. It's scheduled Delivery Day is today, but its 8PM and and there is nothing indicating that the mail was delivered today. The last known date and time tracked was a Depart USPS Sort Facility from two days ago. Should I be worried that my mail was not delivered today? Or are the USPS just slow to update the tracking information on the USPS website?