title: Weird tick spacing when plotting with time on x-axis
body: <p>I'm plotting a <code>pandas</code> time series, which work OK when plotting the timestamps on the x-axis...</p>
  <pre class="lang-py prettyprint-override"><code>import pandas as pd
  import numpy as np
  
  ts = pd.date_range(&quot;2020-01-01&quot;, &quot;2020-01-02&quot;, freq='15T', closed=&quot;left&quot;)
  vals = np.random.rand(len(ts))
  pd.Series(vals, ts).plot()
  </code></pre>
  <p><a href="https://i.stack.imgur.com/dHIrW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dHIrW.png" alt="enter image description here" /></a></p>
  <p>...but which gives me a very unnatural tick spacing when plotting only the time part on the x-axis:</p>
  <pre class="lang-py prettyprint-override"><code>pd.Series(vals, ts.time).plot()
  </code></pre>
  <p><a href="https://i.stack.imgur.com/IoRkw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IoRkw.png" alt="enter image description here" /></a></p>
  <p><strong>How can I turn the x-axis of this second plot into something more human-readable?</strong></p>