MYSQL set timezone in PHP code

How can I change MYSQL TIMEZONE to GMT format like this function in PHP: /SET GMT TIMEZONE/ date_default_timezone_set('Etc/GMT');

My DB class is here:

class DB {
    private static $instance;
    private $MySQLi;

    private function __construct(array $dbOptions){

        $this->MySQLi = @ new mysqli(   $dbOptions['db_host'],
                                        $dbOptions['db_user'],
                                        $dbOptions['db_pass'],
                                        $dbOptions['db_name'] );

        if (mysqli_connect_errno()) {
            throw new Exception('Database error.');
        }

        $this->MySQLi->set_charset("utf8");
    }

    public static function init(array $dbOptions){
        if(self::$instance instanceof self){
            return false;
        }

        self::$instance = new self($dbOptions);
    }

    public static function getMySQLiObject(){
        return self::$instance->MySQLi;
    }

    public static function query($q){
        return self::$instance->MySQLi->query($q);
    }

    public static function prepare($q){
        return self::$instance->MySQLi->prepare($q);
    }

    public static function esc($str){
        return self::$instance->MySQLi->real_escape_string(htmlspecialchars($str));
    }

}

And my queries like this in other files:

DB::query('UPDATE `calendar_data` SET `data` = "'.DB::esc(json_encode($array)).'", `upcoming_time` = "'.date('Y-m-d H:i:s', $upcoming).'", `time_now` = NOW() WHERE `id` = "1"');

Where should I insert my query to the class for run it once?

Thanks!

$this->MySQLi->set_charset("utf8");
$this->MySQLi->query("SET timezone = 'GMT'");

• Doesn't work. If I use NOW(), server time was inserted (GMT-4). Where is a problem???