title: Get time from xts index
body: <p>I have an xts object, x. I want to run a for loop until a certain time, based on the time stamp in the index.</p>
  
  <pre><code>&gt; index(x)
  [1] "2011-10-12 16:44:00 SAST"
  </code></pre>
  
  <p>Lets say I want to run my loop as long as the time in the index is less than say 16:40:00. How do I strip out the time component, given the format of the index above?</p>