def get_album_time(self, round_number=2):
        """
        Retrieves all of the track's length and returns the sum of all
        :param round_number: Int. Number of decimals to round the sum
        :return: Int. Sum of all the track's length
        """
        if not self._track_list:
            self.get_tracks()
        if self._album_time is None:
            album_time = 0.0
            for track in self._track_list:
                album_time += track.get_track_time_minutes()
            self._album_time = round(album_time, round_number)
        return self._album_time