1) After creating the object that you'd like to fade in (or out)go to the next page for Zooming with objects then go to the 15th frame, and insert a KeyFrame.
(The longer of zooming you'd like, the more frames, and vise-versa for faster zooming.)
2) At the 15th frame, change the size of the object.
Note: You could also change the color, as well as the font size!
3) Go back to first frame, and tween it as Shape Tween.