When do electors vote?

[CathKhan]

Say in 1872 when Horace Greeley died before the electors voted so the electors picked their own candidates. Is there a source for the dates of when the electors vote? In a tl I'm working on elsewhere, the winner of an election dies during the lame duck period and my plan is for the party to quickly nominate his Vice-Presidential nominee and another person before the electors have a chance to vote. Is that possible, and if so, as said before, what are the dates?

[J. J.]

I think that it is in December.  The Monday after the second Wednesday according to Wikipedia.

[True Federalist]

Established by law (3 USC 7) as that date, though Congress could choose another if it were so inclined.  I wonder how Bush v. Gore might have turned out had the day been the Tuesday after the first Monday in January instead.