Highcharts will automatically try to find the best format for the current zoom-range. This is done if the xAxis has the type 'datetime'. Next the unit of the current zoom is calculated, it could be one of: second minute hour day week month year This unit is then used find a format for the axis labels. The default patterns are: second: '%H:%M:%S', minute: '%H:%M', hour: '%H:%M', day: '%e. %b', week
![How to get highcharts dates in the x axis?](https://cdn-ak-scissors.b.st-hatena.com/image/square/98d6f053a97a87156775f60757c60865d0f2c47d/height=288;version=1;width=512/https%3A%2F%2Fcdn.sstatic.net%2FSites%2Fstackoverflow%2FImg%2Fapple-touch-icon%402.png%3Fv%3D73d79a89bded)