<?php

function add_acf_columns ( $columns ) {
   return array_merge ( $columns, array ( 
     'duration' => __ ( 'Duration' )
   ) );
 }
 add_filter ( 'manage_tour_posts_columns', 'add_acf_columns' );
 
 /*
 * Add columns to Tours CPT
 */
 function tour_custom_column ( $column, $post_id ) {
   switch ( $column ) {
     case 'duration':
       echo get_post_meta ( $post_id, 'duration', true );
       break;
   }
}
add_action ( 'manage_tour_posts_custom_column', 'tour_custom_column', 10, 2 );

/*
 * Add Sortable columns
 */

function my_column_register_sortable( $columns ) {
	$columns['duration'] = 'duration';
	return $columns;
}
add_filter('manage_edit-tour_sortable_columns', 'my_column_register_sortable' );