Highcharts, Show specific tick on a datetime xaxis type

I have a xAxis which is in datetime format on highcharts.

I send millisecond position of xAxis to place point on chart.

The total time on xAxis is about 2 years.

But I want to show tick only where there are some points (about 6 points).

For the moment, ticks are show at regular interval with the date.

Here is what I have :

And what I need :

thanks,