gistfile1.php

add_filter( 'submit_job_form_fields', 'frontend_add_job_expiry' );
function frontend_add_job_expiry( $fields ) {
  $fields['job']['job_expires'] = array(
    'label' => __( 'Job Expiry', 'job_manager' ),
    'type' => 'text',
    'placeholder' => 'yyyy-mm-dd',
    'priority' => 7
  );
  return $fields;
}