Question about Steffen Time switch

I can't get the random function to work. In addition to pressing the HOUR button for 4 seconds (which brings on the RND indicator), and selecting AUTO ON or AUTO OFF as appropriate, what else do you have to do to get the random generator to function? The French manual says "Pour fonctionner, le générateur aléatoire a besoin que d’une programmation de commutation." What does that mean? In what way is the random function related to the normal programmed time function?