From history.com:
On the Oringinal March date: "The four-month gap was needed in part because of the time it took to count and report votes and to travel to the nation’s capital. However, the lengthy lame-duck period caused problems such as in the aftermath of the 1860 election when seven states left the Union during the long “Secession Winter.” President-elect Abraham Lincoln had no power to act, and outgoing President James Buchanan took no action, leaving the issue for his successor.
As technological advances greatly reduced the times to tabulate votes, report the results and travel, such a long lame-duck period was no longer logistically necessary. As a result, the 20th Amendment, which was ratified on January 23, 1933, moved up Inauguration Day to January 20 and the first meeting of the new Congress to January 3."
From history.com: On the Oringinal March date: "The four-month gap was needed in part because of the time it took to count and report votes and to travel to the nation’s capital. However, the lengthy lame-duck period caused problems such as in the aftermath of the 1860 election when seven states left the Union during the long “Secession Winter.” President-elect Abraham Lincoln had no power to act, and outgoing President James Buchanan took no action, leaving the issue for his successor.
As technological advances greatly reduced the times to tabulate votes, report the results and travel, such a long lame-duck period was no longer logistically necessary. As a result, the 20th Amendment, which was ratified on January 23, 1933, moved up Inauguration Day to January 20 and the first meeting of the new Congress to January 3."