@scompliance,
You can change the thickness of the line by updating endValue within rangeChanged event as shown in code-snippet below.
rangeData[1].endValue = new Date(rangeData[1].startValue.getTime() + (e.chart.axisX[0].viewportMaximum - e.chart.axisX[0].viewportMinimum) / e.chart.axisX[0].bounds.width * 3);
Please take a look at this updated JSFiddle for a working example of the same.
—
Vishwas R
Team CanvasJS