d3js unable to parse json data

I have a json file in the following format

[{
"dayTime1": {
    "timestamp": ["01\/02\/2014 16:59", "02\/02\/2014 16:59", "03\/02\/2014 16:59", "04\/02\/2014 16:59", "05\/02\/2014 16:59", "06\/02\/2014 16:59", "07\/02\/2014 16:59", "08\/02\/2014 16:59", "09\/02\/2014 16:59", "10\/02\/2014 16:59", "11\/02\/2014 16:59", "12\/02\/2014 16:59"],
    "phase1": ["33962", "34273", "45274", "46969", "54078", "53361", "46848", "15377", "15278", "27051", "48179", "30228"],
    "phase2": ["34702", "33259", "39046", "45921", "57756", "58406", "58543", "30094", "31006", "46553", "26914", "47677"],
    "phase3": ["15230", "15304", "15436", "16251", "15232", "19469", "15249", "13478", "16626", "19946", "18332", "16766"]
}

}]

On reading this my d3js code gives out the following error Uncaught TypeError: Object [object Array] has no method 'substring'

I am accessing the values using d.dayTime1.timestamp d.dayTime1.phase1 and so on.

$('#kwh').on('click', function () {
    var endDate = new Date(Date.parse($('#to').val()));
    $('#kwh').prop("disabled",true);

    var margin = {
        top: 50,
        right: 20,
        bottom: 50,
        left: 100
    },
        width = 1000 - margin.left - margin.right,
        height = 400 - margin.top - margin.bottom;

    var parseDate = d3.time.format("%d/%m/%Y %H:%M").parse;

    var x = d3.time.scale().range([0, width]);
    var y = d3.scale.linear().range([height, 0]);

    var xAxis = d3.svg.axis().scale(x)
        .orient("bottom").ticks(15);
    var yAxis = d3.svg.axis().scale(y)
        .orient("left").ticks(10);
     var yAxis1 = d3.svg.axis().scale(y)
        .orient("right").ticks(10);    

    var valueline = d3.svg.line()
            .x(function(d) { return x(d.dayTime1.timestamp); })
            .y(function(d) { return y((d.dayTime1.phase1)/1000); }); 

    var valueline2 = d3.svg.line()
            .x(function(d) { return x(d.dayTime1.timestamp); })
            .y(function(d) { return y((d.dayTime1.phase2)/1000); }); 

    var valueline3 = d3.svg.line()
            .x(function(d) { return x(d.dayTime1.timestamp); })
            .y(function(d) { return y((d.dayTime1.phase3)/1000); });                

    var svg = d3.select("#graph")
        .append("svg")
        .attr("width", width + margin.left + margin.right)
        .attr("height", height + margin.top + margin.bottom)
        .append("g")
        .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

   /* function make_x_axis() {
        return d3.svg.axis()
        .scale(x)
        .orient("yop")
        .ticks(20)
        }*/
    function make_y_axis() {
        return d3.svg.axis()
        .scale(y)
        .orient("left")
        .ticks(10)
        }

    d3.json("<?php echo base_url(); ?>uploads/<?php echo $username; ?>-dayTime1.json", function(error, data) {
        data.forEach(function(d) {
            d.dayTime1.timestamp = parseDate(d.dayTime1.timestamp);
            d.dayTime1.phase1 = +d.dayTime1.phase1;  //<===
            d.dayTime1.phase2 = +d.dayTime1.phase2; // <===
            d.dayTime1.phase3 = +d.dayTime1.phase3; //   <===

        });

        x.domain(d3.extent(data, function(d) {return d.dayTime1.timestamp;}));
        y.domain([0, d3.max(data, function(d) {
                var decValue =  Math.max(d.dayTime1.phase1, d.dayTime1.phase2, d.dayTime1.phase3);
                return (decValue/1000);
    })]);

    svg.append("path")
        .attr("class","line")
/*        .style("stroke", "yellow");*/
        .attr("d", valueline(data));

    svg.append("path")
        .attr("class", "line1")
        .style("stroke", "red")
        .attr("d", valueline2(data));

    svg.append("path")
        .attr("class", "line2")
        .style("stroke", "green")
        .attr("d", valueline3(data));

    svg.append("g") // Add the X Axis
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height + ")")
        .call(xAxis);

    svg.append("g") // Add the Y Axis
        .attr("class", "y axis")
            .call(yAxis);   

    svg.append("g") // Add the Y Axis 1
        .attr("class", "y1 axis")
        .attr("transform", "translate("+width+",0)")
            .call(yAxis1);        

    svg.append("text") // text label for the x axis
        .attr("x", (width/2) )
        .attr("y", height + 50)
        .style("text-anchor", "middle")
        .style("font-weight", "bold")
        .text("Date");        

    svg.append("text")
        .attr("x", -200)
        .attr("y",  -40)    
        .attr("class","leftlegend")
        .style("font-weight", "bold")
        .text("KWH Per Phase");

    });

   /*svg.append("g")
        .attr("class", "grid")
        .attr("transform", "translate(0," + height + ")")
        .call(make_x_axis()
        .tickSize(-height, 0, 0)
        .tickFormat("")
        );*/


    svg.append("g")
    .attr("class", "grid")
    .call(make_y_axis()
    .tickSize(-width, 0, 0)
    .tickFormat("")
    );

});

Is this the right way of accessing it ?