public function maintenance_warning() {
        global $CFG;

        $output = '';
        if (isset($CFG->maintenance_later) and $CFG->maintenance_later > time()) {
            $timeleft = $CFG->maintenance_later - time();
            // If timeleft less than 30 sec, set the class on block to error to highlight.
            $errorclass = ($timeleft < 30) ? 'alert-error alert-danger' : 'alert-warning';
            $output .= $this->box_start($errorclass . ' moodle-has-zindex maintenancewarning m-a-1 alert');
            $a = new stdClass();
            $a->hour = (int)($timeleft / 3600);
            $a->min = (int)(($timeleft / 60) % 60);
            $a->sec = (int)($timeleft % 60);
            if ($a->hour > 0) {
                $output .= get_string('maintenancemodeisscheduledlong', 'admin', $a);
            } else {
                $output .= get_string('maintenancemodeisscheduled', 'admin', $a);
            }

            $output .= $this->box_end();
            $this->page->requires->yui_module('moodle-core-maintenancemodetimer', 'M.core.maintenancemodetimer',
                    array(array('timeleftinsec' => $timeleft)));
            $this->page->requires->strings_for_js(
                    array('maintenancemodeisscheduled', 'maintenancemodeisscheduledlong', 'sitemaintenance'),
                    'admin');
        }
        return $output;
    }