php date_helper.php return utc and local datetime string for db

<?php

if (!function_exists('utc_datetime')) {

    function utc_datetime($datetime = '', $format = 'Y-m-d H:i:s') {
        $time = time();
        if ($datetime !== '') {
            $time = strtotime($datetime);
        }

        $date = new DateTime();
        $date->setTimezone(new DateTimeZone('UTC'));
        $date->setTimestamp($time);
        return $date->format($format);
    }

}

if (!function_exists('local_datetime')) {

    function local_datetime($datetime = '', $timezone = 'Asia/Ulaanbaatar', $format = 'Y-m-d H:i:s') {
        $time = time();
        if ($datetime !== '') {
            $time = strtotime($datetime);
        }

        $date = new DateTime();
        $date->setTimezone(new DateTimeZone($timezone));
        $date->setTimestamp($time);
        return $date->format($format);
    }

}
?>

USAGE

<?php

if (!defined('BASEPATH'))
    exit('No direct script access allowed');

class boroo extends BaseController {

    function __construct() {
        parent::__construct();
    }

    public function hello() {
        global $RTR;

        $expire = (7 * 24 * 60 * 60);
        $this->input->set_cookie("time", time(), $expire);
        $time = $this->input->cookie('time');
        $timezone = $this->getZone();
        $format = 'Y-m-d H:i:s';

        $this->load->helper('date');
        date_default_timezone_set('Asia/Ulaanbaatar');
        $time = strtotime(utc_datetime('2013-09-10 10:30:45'));
        $newtime = mktime(date('H',$time), date('i',$time), date('s',$time));
        $date = date($format, $newtime);
        echo $date;
        exit;
        echo local_datetime('2013-09-10 10:30:45') . "=>" . utc_datetime('2013-09-10 10:30:45');
        exit;
        $data['message'] = 'Date is ' . $dateStr . ', IP is ' . $this->getIp();
        $this->load->view($RTR->fetch_directory() . $RTR->fetch_class() . '/hello', $data);
    }

}

or

$date = new DateTime('2013-09-10 10:30:45');
        $dateStr = date("Y-m-d H:i:s", strtotime('+5 minutes', $date->getTimestamp()));
        echo $dateStr;
        exit;