That’s what I got from Wikipedia. Duh me...
It sounds like where I went astray is that the designated December date is not fixed by the Constitution but instead by statute. This being the case Congress could change the statute. However, a statute change if it would pass would have to be able to be able to muster a veto over ride number of votes.
The thing is, Congress doesn't have to act at all. The states already have the power to act independently.
Rubio is misinterpreting the problem. It's not about "giving" the Electoral College more time to vote -- that's just a stall to let the states have more time to count the mailed-out ballots. It's about letting the state legislatures solve the problem themselves by convening a special session to vote to appoint the Electors when and if the time limit approaches and there is no settled count.
The power of the state legislatures to choose the method of selecting Electors is Supreme law of the land. No Rubio legislation can override that. Any state legislature that wants to can appoint their Electors directly, even if it is weeks before Rubio's January 1 date.
-PJ