Relative time helper like twitter in JavaScript

relative_time.js

var relative_time = function(timestamp, relative_to) {
  if (timestamp === null || timestamp === undefined)
    return "";

  var delta, relative_is_future, t;

  if (!relative_to)
    relative_to = parseInt(new Date().getTime() / 1000);

  if ($.type(timestamp) !== "number")
    timestamp = timestamp.getTime() / 1000;

  delta = timestamp - relative_to;
  relative_is_future = delta > 0 ? true : false;
  delta = Math.abs(delta);
  if (delta < 60) {
    t = "less than a minute";
  } else if (delta < 120) {
    t = "about a minute";
  } else if (delta < 2700) {
    t = (parseInt(delta / 60)).toString() + " minutes";
  } else if (delta < 5400) {
    t = "about an hour";
  } else if (delta < 86400) {
    t = "about " + (parseInt(delta / 3600)).toString() + " hours";
  } else if (delta < 172800) {
    t = "one day";
  } else {
    t = (parseInt(delta / 86400)).toString() + " days";
  }
  if (relative_is_future) {
    return "in " + t;
  } else {
    return t + " ago";
  }
};