Custom Time Ticks

HTML

<div class="container">

    <div class="jumbotron">

    </div>
    <svg id="visualisation" width="1000" height="500"></svg>

    <div id="svgdataurl"></div>
</div>

CSS

<link href="http://getbootstrap.com/dist/css/bootstrap.min.css" rel="stylesheet">

    <link href="http://getbootstrap.com/examples/justified-nav/justified-nav.css" rel="stylesheet">

JavaScript

var lineData = [{
    time: 1425299975000,
    y: 20
}, {
    time: 1425472775000,
    y: 10
}, {
    time: 1425512375000,
    y: 40
}, {
    time: 1425598775000,
    y: 5
}, {
    time: 1425685175000,
    y: 45
}, {
    time: 1425771575000,
    y: 43
}, {
    time: 1425857975000,
    y: 23
}, {
    time: 1425944375000,
    y: 12
}, {
    time: 1426030775000,
    y: 31
}, {
    time: 1426117175000,
    y: 76
}, {
    time: 1426203575000,
    y: 56
}, {
    time: 1426289975000,
    y: 78
}, {
    time: 1426376375000,
    y: 89
}, {
    time: 1426462775000,
    y: 98
}, {
    time: 1426549175000,
    y: 56
}, {
    time: 1426635575000,
    y: 34
}, {
    time: 1426721975000,
    y: 56
}, {
    time: 1426808375000,
    y: 60
}, {
    time: 1426894775000,
    y: 22
}, {
    time: 1426981175000,
    y: 66
}, {
    time: 1427067575000,
    y: 44
}, {
    time: 1427153975000,
    y: 11
}, {
    time: 1427240375000,
    y: 43
}, {
    time: 1427326775000,
    y: 98
}, {
    time: 1427413175000,
    y: 34
}, {
    time: 1427499575000,
    y: 10
}, {
    time: 1427585975000,
    y: 20
}, {
    time: 1427672375000,
    y: 34
}, {
    time: 1427758775000,
    y: 11
}, {
    time: 1427845175000,
    y: 55
}, {
    time: 1427931575000,
    y: 33
}, {
    time: 1428017975000,
    y: 56
}, {
    time: 1428104375000,
    y: 77
}, {
    time: 1428190775000,
    y: 101
}, {
    time: 1428277175000,
    y: 115
}, {
    time: 1428363575000,
    y: 60
}, {
    time: 1428449975000,
    y: 15
}];

var format = d3.time.format("%d/%m");

function customTickFunc (t0, t1, step)
{    
    var startTime = new Date(t0),
        endTime= new Date(t1), times = [];
   endTime.setUTCDate(endTime.getUTCDate() + 1);
    while (startTime < endTime) {
      startTime.setUTCDate(startTime.getUTCDate() + 2);
           times.push(new Date(startTime));
    }
    return times;
}

var vis = d3.select('#visualisation'),
    WIDTH = 1000,
    HEIGHT = 500,
    MARGINS = {
      top: 20,
      right: 20,
    ...