I believe what you might be referring to is that if you choose 120 days it still reads the current month ...

The code is designed to show the current month based on the define ...

You can alter this in the module using an override for the file:

/includes/modules/new_products.php

and changing this code to what you like ...
PHP Code:
  if ($new_products->RecordCount() > 0) {
    if (isset(
$new_products_category_id) && $new_products_category_id != 0) {
      
$category_title zen_get_categories_name((int)$new_products_category_id);
      
$title '<h2 class="centerBoxHeading">' sprintf(TABLE_HEADING_NEW_PRODUCTSstrftime('%B')) . ($category_title != '' ' - ' $category_title '' ) . '</h2>';
    } else {
      
$title '<h2 class="centerBoxHeading">' sprintf(TABLE_HEADING_NEW_PRODUCTSstrftime('%B')) . '</h2>';
    }
    
$zc_show_new_products true;
  } 
What Kim is referring to is the setting for the Actual New Products that are displayed based on when you added these products and what date period they should cover ...