diff 将返回一个DateInterval对象，该对象包含有关两个日期之间的差的详细信息。您只是在尝试回显无效的对象。执行 var_dump（）来查看对象的属性：

diff is going to return a DateInterval object full of good information about the difference between your two dates. You're just trying to echo that object which won't work. Do a var_dump() to see the object's properties:

$time = "2016-09-15 20:10:35";
$timenow = "2016-09-15 20:40:42";

$time = new DateTime($time);
$timenow = new DateTime($timenow);

$interval = $timenow->diff($time);
var_dump($interval);

然后，您可以回显以下属性：

Then you can echo out the properties like:

echo $interval->i; // minutes
// 30

http://php.net/manual/en/class.dateinterval.php