When you submit the form, the value is presented with debug_dump(), so strings are quoted and array values listed.

: :
: - Stop the submitted form from bring processed
: - Don't process the form, redirect to another page (e.g. login after session timeout), and remember the values for when they return.

or back to examples 

<?php
	$field = new form_field_time($form, 'Time');
	$field->invalid_error_set('Your time does not appear to be correct.');
	$field->required_error_set('Your time is required.');
	$field->min_time_set('Your time has to be after 3am.', '03:00');
	$field->max_time_set('Your time cannot be set in the future.', time());
?>