It would be more of a shot timer than a pause. You will need to add an instance 'int shotTimer' to the Turret class, set it to some small number (maybe some number between 25 and 50) every time a bullet is created and only create one when the timer is zero (decreasing the timer, if greater than zero, every act).

Make a new variable for your turret classes. private int cooldown or something. Then add one to it every act and put an if-statement thats makes sure you can only fire a bullet when "cooldown" is above x. Then when you shoot a bullet make sure to set "cooldown" to 0. EDIT: The same idea as danpost's.