how_much_netflix.js

// how_much_netflix.js
// A script that looks through your Netflix viewing activity and
// tallys up how much time you've spent watching Netflix
//
// INSTRUCTIONS TO USE:
// Open https://www.netflix.com/WiViewingActivity and the developer console
// Copy and paste this script into the developer console and press enter
//
(function() {
  var fetchAllViewedItems = function() {
    var deferred = jQuery.Deferred();
    var viewedItems = [];
    (function fetchPage(page) {
      jQuery.getJSON('https://www.netflix.com/api/shakti/b6260b85/viewingactivity?pg=' + page).done(function(json) {
        viewedItems = viewedItems.concat(json.viewedItems);
        console.log('Fetched %s viewed items', viewedItems.length);
        if (json.viewedItems.length == json.size) {
          fetchPage(++page);
        } else {
          deferred.resolve(viewedItems);
        }
      }).fail(deferred.reject);
    })(0);
    return deferred.promise();
  };
  fetchAllViewedItems().then(function(viewedItems) {
    var totalTime = viewedItems.reduce(function(runningTotal, viewedItem) {
      return runningTotal + viewedItem.bookmark;
    }, 0);
    var days = Math.floor(totalTime / 60 / 60 / 24);
    var hours = Math.floor((totalTime / 60 / 60) % 24);
    var minutes = Math.round((totalTime / 60) % 60);
    console.log('According to your viewing history, you have cumulatively watched %i days, %i hours and %i minutes of Netflix', days, hours, minutes);
  });
})();

I've been through all the modified scripts I can find and this is the only one that works still, Netflix change their code too much to justify any real effort in fixing the others so if you want to get this script to work, the simplest way is to open the developer console and go to the network tab, scroll down one page on the viewing history page to see what the API url should be, and correct the script.

Another thing worth noting, is that the figures it gives out are seriously inaccurate if you like to rewatch shows. Each show you watch will only appear once in that page no matter how many times you watch it.

That always changing number is build identifier for Netflix API, it probably changes with every new build of their API. You can find current one in source of the page, search for BUILD_IDENTIFIER.