When processing an in-state shipment with the PB Shipping API USPS carrier using Priority Express Mail service, the expected commitment delivery date is 1 day, but the label prints as 2-day delivery.
Delivery transit time information is based on the Origin and Destination Postal Codes, as well as the time of day the label is printed. One-day delivery commitments assume that the package will be at the Post Office by a certain time.
This does not mean that it will not be delivered within 1 day, but due to timing it may only guarantee 2-day delivery.
This is expected behavior. No further action is necessary.
UPDATED: June 04, 2020