title: Bokeh: Bad date format?
body: <p>would anyone advise me how to adjust the X axis to better display the date on this graph?</p>
  
  <p><img src="https://i.stack.imgur.com/kfz91.jpg" alt="Graph: "></p>
  
  <p><img src="https://i.stack.imgur.com/r7opM.jpg" alt="Data: "></p>
  
  <hr>
  
  <pre><code>from math import pi
  import pandas as pd
  from bokeh.io import show
  from bokeh.models import LinearColorMapper, BasicTicker, PrintfTickFormatter, ColorBar
  from bokeh.plotting import figure
  
  #cesta k souboru
  path = "C://Users//Zemi4//Desktop//zpr3//all2.csv"
  
  #nacteni dataframu
  data = pd.read_csv(path, delimiter = ",")
  
  data['Cas'] = data['Cas'].astype(str)
  data = data.set_index('Cas')
  data.columns.name = 'Mistnost'
  
  times = list(data.index)
  rooms = list(data.columns)
  
  df = pd.DataFrame(data.stack(), columns=['float']).reset_index()
  
  colors = ['#440154', '#404387', '#29788E', '#22A784', '#79D151', '#FDE724', '#FCFEA4', '#FBA40A', '#DC5039']
  mapper = LinearColorMapper(palette=colors, low=df.float.min(), high=df.float.max())
  
  TOOLS = "hover,save,pan,box_zoom,reset,wheel_zoom"
  
  p = figure(title="Heatmap ({0} - {1})".format(times[0], times[-1]),
             x_range=times, y_range=list(reversed(rooms)),
             x_axis_location="above", plot_width=1500, plot_height=900,
             tools=TOOLS, toolbar_location='below',
             tooltips=[('Time: ', '@Cas'), ('Temperature: ', '@float'), ('Room: ', '@Mistnost')],
             x_axis_type='datetime')
  
  p.grid.grid_line_color = None
  p.axis.axis_line_color = None
  p.axis.major_tick_line_color = None
  p.axis.major_label_text_font_size = "5pt"
  p.axis.major_label_standoff = 0
  p.xaxis.major_label_orientation = pi / 3
  
  p.rect(x="Cas", y="Mistnost", width=1, height=1,
         source=df,
         fill_color={'field': 'float', 'transform': mapper},
         line_color=None)
  
  color_bar = ColorBar(color_mapper=mapper, major_label_text_font_size="5pt",
                       ticker=BasicTicker(desired_num_ticks=len(colors)),
                       formatter=PrintfTickFormatter(format="%f"),
                       label_standoff=6, border_line_color=None, location=(0, 0))
  p.add_layout(color_bar, 'right')
  
  show(p)      # show the pl
  </code></pre>