日期默认时区错误时间

Question

Im trying to figure out why i'm getting the wrong time, this is my code:

date_default_timezone_set("Europe/Amsterdam"); //Use the time of amsterdam
$date = new DateTime();
$date->modify("+".$tijd." minutes"); //Add the time in minutes to current time.
$datum = $date->format('Y-m-d H:i:s');

So when $tijd is set to 10, $datum returns this: 2015-02-28 14:49:00 But in Amsterdam the time is 14:10 at the moment (around that). So it should give something like 2015-02-28 14:20:00.

So what am i doing wrong since this is kinda weird, Thanks in advance!

EDIT: This is my full-code: public function jail($tijd, $id){

date_default_timezone_set("Europe/Amsterdam"); //Use the time of amsterdam
$date = new DateTime();
$date->modify("+".$tijd." minutes"); //Add the time in minutes to current time.
$datum = $date->format('Y-m-d H:i:s');

$conn = $this->conn;

$jail = $conn->prepare('UPDATE gebruikers
                          SET jail = :jail
                          WHERE id = :id');

$uitvoeren = $jail->execute(array(
    ':jail'  => $datum, 
    ':id'  => $id));

if($uitvoeren){
    return true;
} else {
    return false;
}

}

And then in another PHP file:

$user = new user;

$tijd = 10;
$id = 1;

$gevangenis = $user->jail($tijd, $id);

if($gevangenis){
    echo 'Gelukt!';
} else {
    echo 'Mislukt!';
}