24 hour minute step series

HTML

<h1 id="title">24 Hour Minute Series</h1>
<input type="number" id="step" value="30" />
<input type="submit" id="byBtn" value="Generate Series" onclick="generate_series(parseInt(document.getElementById('step').value,10))" />
<div id="series">
</div>

JavaScript

function generate_series(step) {
  var dt = new Date(1970, 0, 1, 0, 0, 0, 0),
    el = document.getElementById("series")

  while (el.firstChild)
    el.removeChild(el.firstChild);

  while (dt.getDate() == 1) {
    var point = dt.toLocaleTimeString('en-US');
    dt.setMinutes(dt.getMinutes() + step);

    var item = document.createElement("div");
    item.innerText = point;
    el.appendChild(item);

  }
}