How Often Should the Congress Assemble?
The United States shall guarantee to every State in this Union a Republican Form of Government and The Congress shall assemble at least once in every Year.
ARTICLE IV: STATES
Section 4
The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened), against domestic Violence.
The Congress shall assemble at least once in every Year, and such Meeting shall be on the first Monday in December, unless they shall by Law appoint a different Day.
https://www.heritage.org/... !/articles/1