def create_time_labels(self):
        """Create the time labels, but don't plot them yet.

        Notes
        -----
        It's necessary to have the height of the time labels, so that we can
        adjust the main scene.

        Not very robust, because it uses seconds as integers.
        """
        min_time = int(floor(min(self.data.axis['time'][0])))
        max_time = int(ceil(max(self.data.axis['time'][0])))
        n_time_labels = self.parent.value('n_time_labels')

        self.idx_time = []
        self.time_pos = []
        for one_time in linspace(min_time, max_time, n_time_labels):
            x_label = (self.data.start_time +
                       timedelta(seconds=one_time)).strftime('%H:%M:%S')
            item = QGraphicsSimpleTextItem(x_label)
            item.setFlag(QGraphicsItem.ItemIgnoresTransformations)
            self.idx_time.append(item)
            self.time_pos.append(QPointF(one_time,
                                         len(self.idx_label) *
                                         self.parent.value('y_distance')))
Create the time labels, but don't plot them yet.

        Notes
        -----
        It's necessary to have the height of the time labels, so that we can
        adjust the main scene.

        Not very robust, because it uses seconds as integers.