Leaders are elected every 4 years.
You can read about this in our Constitution:
The Convention of this International Union shall meet every four years and shall convene at such time and place as the International Executive Board may determine upon the recommendation of the International President.
Section 2. Special Conventions may be called upon order of the International Executive Board to convene at such time and place as the Board may determine, and any and all business, including appeals from suspensions and decisions of the International Executive Board, may come before such Special Convention unless specifically limited by the call. Notice of such call shall be given to each Local Union at least 60 days prior to the date of the Special Convention along with the number of delegates to which said Local Union is entitled. All other provisions of this Article shall control all Special Conventions.