Gravity Forms - Custom Export Column

functions.php

<?php
add_filter( 'gform_export_fields', 'add_step_updated', 10, 1 );
function add_step_updated( $form ) {
	array_push( $form['fields'], array( 'id' => 'step_updated', 'label' => __( 'Step Last Updated', 'gravityforms' ) ) ); 
	return $form;
}

add_filter( 'gform_export_field_value', 'set_step_updated', 10, 4 );
function set_step_updated( $value, $form_id, $field_id, $entry ) {
	switch ( $field_id ) {
		case 'step_updated':
			$duration = time() - $entry['workflow_timestamp'];
			$value = gravity_flow()->format_duration( $duration );
			break;
	}
	return $value;
}
?>