This applies to the Angular-nvD3 charting directive for Angular JS.

To create custom tooltips rather than NVD3’s built-in “interactiveGuideline” we can do something like the following to create some HTML of our own to display within the tooltip. In this case I am pulling out the timestamp and value of the point from my dataseries (d.point is the current point being hovered over) and also the series name of the current series (d.series[0].key)…

$scope.options = {
    chart: {
        useInteractiveGuideline: false,
        tooltip: {
            contentGenerator: function(d) {
                var str = '';
                //console.log(d);
                str += ('<div style="font-weight:bold; margin:auto; text-align:center;">' +d3.time.format('%Y-%m-%d %H:%M')(new Date(d.point.x)) + '</div>');
                str += ('' + d.series[0].key + ': ');
                str += ('' + d.point.y +'');
                return str;
            }
        }
    }
}