The commissioners shall hold their first meeting at the prescribed time and place, and if a time or place be not prescribed they shall hold their first meeting at some convenient place within the limits of the special Act on the third Wednesday next after the commencement thereof, or, if the first body of commissioners be not named in the special Act, on the first Wednesday after the first election of commissioners, or as soon after such periods respectively as conveniently may be, at the hour of ten of the clock in the forenoon, and shall proceed to put this and the special Act into execution.