Calculate time difference in seconds between 2 dates PHP : <p>I have to 2 dates values in PHP, </p>

<pre><code>start_date_time = "2018-03-15T20:39:06Z"

end_date_time = "2018-03-17T12:42:08Z"

duration = ?  // in seconds
</code></pre>

<p>I actually want to get total time in seconds. Please help</p>
