The 20th amendment changed the days for meetings in congress for the President and vice president.
Well, the 20th amendment was mostly created to prevent the 'Lame Duck' period. The Lame Duck period is when Congress holds a meeting for a new president, but the meeting is before the new president's term. The 20th amendment prevents this. The 20th amendment changes the President and vice president's new term from March 4th to January 20th. It also changes the new congress meeting from March 3rd to January 3rd.
Why was the 20th amendment created you ask?
The 20th amendment was ratified on March 4th, 1939.