title: data difference in `as.POSIXct` with Excel
body: <p>My actual data looks like:</p>
  
  <pre><code>8/8/2013 15:10
  7/26/2013 10:30
  7/11/2013 14:20
  3/28/2013 16:15
  3/18/2013 15:50
  </code></pre>
  
  <p>When I read this from the excel file, R reads it as:</p>
  
  <pre><code>41494.63
  41481.44
  41466.60
  41361.68
  41351.66
  </code></pre>
  
  <p>So I used <code>as.POSIXct(as.numeric(x[1:5])*86400, origin="1899-12-30",tz="GMT")</code> and I got:</p>
  
  <pre><code>2013-08-08 15:07:12 GMT
  2013-07-26 10:33:36 GMT
  2013-07-11 14:24:00 GMT
  2013-03-28 16:19:12 GMT
  2013-03-18 15:50:24 GMT
  </code></pre>
  
  <p>Why there is a difference in time? How to overcome it?</p>