var config = { attributes: true, childList: true, characterData: true };
var target = document.body;
var timer;

// create an observer instance
var observer = new MutationObserver(function(mutations) {

   // fired when a mutation occurs
   timer = setTimeout(function () {

      _3rd_party_callback();


   }, 500);

});

observer.observe(target, config);

observer.disconnect()
  _3rd_party_callback();
  observer.observe(target, config);