chamilo-lms2/main/inc/lib/formvalidator/Rule/CompareDateTimeText.php

<?php
/* For licensing terms, see /license.txt */

/**
 * QuickForm rule to compare 2 dates
 */
class HTML_QuickForm_Rule_CompareDateTimeText extends HTML_QuickForm_Rule_Compare
{
    /**
     * Validate 2 dates
     * @param string $operator The operator to use (default '==')
     * @return boolean True if the 2 given dates match the operator
     */
    function validate($values, $operator = null) {
    	$datetime1 = api_strtotime($values[0]);
        $datetime2 = api_strtotime($values[1]);

        if (strpos($operator, 'allow_empty') !== false) {
            $operator = str_replace('allow_empty', '', $operator);
            if (!$datetime2 || empty($datetime2)) {
                return true;
            }
        }
		$result =  parent::validate(array($datetime1, $datetime2), $operator);
        return $result;
    }
}