Limit labels number on Chart.js line chart

Try adding the options.scales.xAxes.ticks.maxTicksLimit option:

xAxes: [{
    type: 'time',
    ticks: {
        autoSkip: true,
        maxTicksLimit: 20
    }
}]

For concreteness, let's say your original list of labels looks like:

["0", "1", "2", "3", "4", "5", "6", "7", "8"]

If you only want to display every 4th label, filter your list of labels so that every 4th label is filled in, and all others are the empty string (e.g. ["0", "", "", "", "4", "", "", "", "8"]).