The electoral college meets on the “first Monday after the second Wednesday in december”. Don’t ask
Me why do many of our nation’s dates are set forth in this manner — ha — but anyway it’s fixed
To hazard a guess...
It's a function of counting days from the first Tuesday after the first Monday in November -- which is Election Day. And the number of days reserved for each step in the electoral sequence would reflect the distances involve in a frontier nation where the only mode of communication and travel was by horseback.
They couldn't specify dates because it would occasionally fall on a Sunday -- which was reserved for a more important activity than elections.