title: Set datetime measure unit in Highcharts
body: <p>I setup my column chart with 3 data points. Each x value is a datetime value - different hour within one day.</p>
  
  <pre><code>$(function () {
      $('#container').highcharts({
          chart: {
              type: 'column'
          },
  
          xAxis: {
              type: 'datetime'
          },
          series: [{
              data: [
                  [Date.UTC(2013, 5, 1, 0, 0, 0), 1], 
                  [Date.UTC(2013, 5, 1, 2, 0, 0), 1], 
                  [Date.UTC(2013, 5, 1, 4, 0, 0), 1]
              ]
          }]
      });
  });
  </code></pre>
  
  <p>This is my example: <a href="http://jsfiddle.net/CqkUc/1/" rel="nofollow">http://jsfiddle.net/CqkUc/1/</a></p>
  
  <p>My problem is that every column tooltip shows the same date, and i want them to show different hours. I know that i can use the tooltip formatter function, but i think there might be a way to force xAxis unit to be an hour.</p>