function genesis_post_modified_date_shortcode( $atts ) {

  $defaults = [
    'after'          => '',
    'before'         => '',
    'format'         => get_option( 'date_format' ),
    'label'          => '',
    'relative_depth' => 2,
  ];

  $atts = shortcode_atts( $defaults, $atts, 'post_modified_date' );

  if ( 'relative' === $atts['format'] ) {
    $display  = genesis_human_time_diff( get_the_modified_time( 'U' ), current_time( 'timestamp' ), $atts['relative_depth'] );
    $display .= ' ' . __( 'ago', 'genesis' );
  } else {
    $display = get_the_modified_time( $atts['format'] );
  }

  $output = sprintf( '<time %s>', genesis_attr( 'entry-modified-time' ) ) . $atts['before'] . $atts['label'] . $display . $atts['after'] . '</time>';

  
/**
 * Change the output of the post_modified_date shortcode.
 *
 * @since 2.1.0
 *
 * @param string $output Markup containing post last modification date.
 * @param array  $atts {
 *     Shortcode attributes after merging with default values.
 *
 *     @type string $after Output after date.
 *     @type string $before Output before date.
 *     @type string $format Date format, could be 'relative'.
 *     @type string $label Text following 'before' output, but before date.
 * }
 */
  return apply_filters( 'genesis_post_modified_date_shortcode', $output, $atts );

}