Final answer:
The Congress must meet at least once every year, as stated in the Constitution.
Step-by-step explanation:
The Congress must meet at least once every year, as stated in the Constitution. Specifically, the first meeting of Congress begins at noon on January 3 of each year unless otherwise specified by the members.
This requirement is established in the Constitution's Article I, Section 4, and is further clarified by the 20th Amendment, which changed the opening day of Congress from the first Monday in December to January 3.