code: function nextValidStart(schedules) {
      var latest;
      for(var i = 0, len = schedules.length; i < len; i++) {
        var end = schedules[i].range[1];
        latest = !latest || end < latest ? end : latest;
      }
  
      return latest;
    }
docs: Determines the earliest time that a schedule goes invalid which is the
  time that should be used to update resource ranges from.