The phrase "to shoot off" means to start or begin something with great speed, energy and enthusiasm. It can also mean to fire a gun or missile quickly and powerfully in one direction. The term is often used figuratively when describing an event that begins with excitement and intensity. For example, if someone says they are going to "shoot off" their fireworks display at midnight, it means the show will start as soon as the clock strikes twelve with great fanfare and spectacle.