Adding and Deleting Timed Structure Frames
Right-click a timed structure border and select Add Frame After or Before from the shortcut menu to add a frame. You also can right-click the border between two frames and select Insert Frame from the shortcut menu to insert a frame between two frames.
To delete a timed structure frame, right-click the bottom or top structure border of the frame and select Delete This Frame from the shortcut menu. If only one frame exists, you cannot delete the frame.