IntervalBarItem change label

I have a IntervalBarSeries with some IntervalBarItems. So, to include IntervalBarItems, I Need to convert DateTime into double. Now I have an ugly double-Value (the End-Value) on my BarItems. By changin the Title-Option nothing happens. Is the any possibility to Change the text on my Items?

IntervalBarItem item = new IntervalBarItem

                    {
                        Start = OxyPlot.Axes.DateTimeAxis.ToDouble(data.startTime,
                        End = OxyPlot.Axes.DateTimeAxis.ToDouble(data.endTime),
                        CategoryIndex = i,

                        Title = data.TimeSpanPercental + "%"

                    };