timedelta in QSTK
<p>I am going through QSTK and in tutorials they use <code>datetime.timedelta</code>
I am curios what is the purpose of such command in stock related environment. I found some articles on what <code>timedelta</code> is but clearly I am not grasping it since I am clueless what this means:</p>

<pre><code>timeofday= datetime.timedelta(hours=16)
timestamps = du.getNYSEdays(startday,endday,timeofday)
</code></pre>

<p>What is a purpose of timedelta as an argument for QSTK or in general.</p>
