Hi Clem,
Add following code snippet to your theme functions.php to display last modified on sidebar of the listing detail page.
// Show last updated on listing detail page
function gd_custom_modified_date_on_listing_detail() {
global $post;
if ( !empty( $post->post_modified ) && $post->post_modified != '0000-00-00 00:00:00' ) {
$date = date_i18n( get_option('date_format'), strtotime( $post->post_modified ) );
$time = date_i18n( get_option('time_format'), strtotime( $post->post_modified ) );
$date_time = $date . ' @ ' . $time;
echo '<div class="geodir_more_info geodir-last-updated" style="clear:both;"><span class="geodir-i-time"><i class="fa fa-clock-o"></i>' . __( 'Last Updated:', 'geodirectory' ) . ' </span>' . $date_time . '</div>';
}
}
add_action( 'geodir_after_edit_post_link', 'gd_custom_modified_date_on_listing_detail', 20 );
Kiran