code: function(timingCategory, timingVar, timingValue, options) {
        if(!timingCategory || !timingVar || typeof timingValue === 'undefined') {
          warn('timing: `timingCategory`, `timingVar`, and `timingValue` are required.');
        } else if (typeof timingValue !== 'number') {
          warn('event: expected `timingValue` to be a Number.');
        } else {
          _set.call(this, 'send', 'timing', timingCategory, timingVar, timingValue, options);
        }
  
        return this;
      }
docs: https://developers.google.com/analytics/devguides/collection/analyticsjs/user-timings