U.S. District Judge Emmet Sullivan on Tuesday had ordered the sweep in response to lawsuits by groups including Vote Forward, the NAACP, and Latino community advocates.
Affected by the order were processing centers in central Pennsylvania, northern New England, greater South Carolina, south Florida, Colorado, Wisconsin and parts of Illinois, Arizona, Alabama and Wyoming, as well as the cities of Atlanta, Houston, Philadelphia, Detroit.
Sullivan ordered postal officials to complete the inspections by 3 p.m. ET (2000 GMT) and certify by 4:30 p.m. ET (2130 GMT) that no ballots were left behind.
Lawyers for the USPS told Sullivan in a court filing that the agency was not able to complete the sweeps by 4:30 p.m. but was "working as expeditiously as possible to comply with this court's orders while recognizing physical and operational limitations and the need to avoid disrupting key activities on Election Day."