title: labels to the axis - conver int (second) to hours
body: <p>How can I make axis labels in the HOURS: MINUTES format (10:00 for example), if the data on the axis are represented as integers in the range [0...N]?</p>
  
  <p>For example:</p>
  
  <pre><code>range [0..43200]
  axis labels: 00:00 04:00 08:00 12:00 
  </code></pre>
  
  <p>seconf example:</p>
  
  <pre><code>range [28800..172800]
  axis labels: 08:00 16:00 24:00 08:00 16:00 24:00 
  </code></pre>
  
  <p>When I use code:</p>
  
  <pre><code>set xdata time
  set format x "%H:%M"
  </code></pre>
  
  <p>it does not work correctly  :(</p>