Storefront change categories to be ordered by date.

functions.php

/**
 * Alters the output of the homepage product categories on the Storefront theme
 * Affects the storefront_product_categories_args filter in /inc/structure/template-tags.php
 */

function rk_display_four_home_product_categories( $args ) {

	// Sets the categories to be ordered by date, instead of name
	$args['orderby'] = 'date';

	// Output
	return $args;

}
add_filter( 'storefront_product_categories_args', 'rk_display_four_home_product_categories' );