It's unclear what you are trying to do with both on clicked and every X seconds at the same time. I thought your issue was modifying the number of seconds. What do you mean by on click and every X seconds ? Do you mean while mouse button is being held down then every X seconds it should fire ? When you click the mouse it should toggle on firing mode for the dragon until you click again ?
Note in general you can't use them both together regardless of what you are trying to do because on clicked is a trigger once event so the every X seconds will not keep running constantly inside it. So really depends what you are tryin to achieve with the gameplay.