1875
Resumption Act
The Specie Payment Resumption Act names 1 January 1879. This is not the day payments resume.

The Specie Payment Resumption Act of 1875 set the date: 1 January 1879. On that later day the United States was to resume specie payments on United States Notes.
Naming the date is not the resumption. The gap between greenbacks and gold is still open. The operational close of that gap is 1879.