…Change the excerpt length in the frontpage columns ?

Hi peeps,
Well, all is in the title ! In the Nirvana setting there is no option to modify the excerpt length of the columns in the front page.
I tried to add this code in functions.php but nothing changed.

<?php function new_excerpt_length($length) {
 return 20;
}
add_filter('excerpt_length', 'new_excerpt_length');
?> 

I think I don’t have the good names of functions for the cryout column.

Please anyone help ! 🙂
You will be reward with all my gratitude !