[Haskell-beginners] Setting x-range in haskell-chart

Hey, I plot a chart where I use LocalTime for the x plot value. I want to define what the range of the x axis is. So I try: layout1_bottom_axis . laxis_generate .~ scaledAxis def (xmin,xmax) where xmin, xmax :: LocalTime. This fails with: No instance for (RealFloat LocalTime) Anyone knows how I set the xrange correctly in chart? Thanks! Nathan