Highstock highcharts irregular data gets wrong x-scale

You will need to set the xAxis.ordinal property to false, this is true by default. True value indicates the points should be placed at fixed intervals w.r.t space (pixels), and False changes points to be placed at fixed intervals w.r.t. time

xAxis: {       
    ordinal: false
}

Linear x-axis | Highstock @ jsFiddle