PHP: add seconds to a date

Given the fact that $adate is a timestamp (if that's the case), you could do something like this:

$duration = 674165;
$result_date = strtotime(sprintf('+%d seconds', $duration), $adate);
echo date('Y-m-d H:i:s', $result_date);

Just use some nice PHP date/time functions:

$adate="Tue Jan 4 07:59:59 2011";
$duration=674165;
$dateinsec=strtotime($adate);
$newdate=$dateinsec+$duration;
echo date('D M H:i:s Y',$newdate);

If you are using php 5.3+ you can use a new way to do it.

<?php 
$date = new DateTime();
echo $date->getTimestamp(). "<br>";
$date->add(new DateInterval('PT674165S')); // adds 674165 secs
echo $date->getTimestamp();
?>