How to calculate the time difference between two timestamps in php?

$start_date = new DateTime('2007-09-01 04:1058');
$since_start = $start_date->diff(new DateTime('2012-09-11 10:25:00'));
echo $since_start->days.' days total<br>';
echo $since_start->y.' years<br>';
echo $since_start->m.' months<br>';
echo $since_start->d.' days<br>';
echo $since_start->h.' hours<br>';
echo $since_start->i.' minutes<br>';
echo $since_start->s.' seconds<br>';

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