[Solved]-Highcharts (Highstock) how to manually set the navigator selected range-Highcharts

as the comment said ,you should use xaxis[0]:

chart.xaxis[0].setextremes(min, max,[boolean redraw], [mixed animation]);

fiddle1

also, you can use xaxis.range when initing your chart:

$('#container').highcharts('stockchart', {
    xaxis: {
        range: 6 * 30 * 24 * 3600 * 1000 // six months
    },
}

fiddle2