title: Convert Data Frame Start/Stop times into percentage bins
body: <p>I want to convert a dataframe of start/end (or on/off) times into a second dataframe with percentages of total 'on time' per some arbitrary time period. In this case, that time period is an hour. I've written a very inefficient solution involving loops, and am looking for a better solution.</p>
  
  <pre><code>df1
  
  | Start               | End                 |
  |---------------------|---------------------|
  | 2020-02-01T00:00:00 | 2020-02-01T02:40:00 |
  | 2020-02-01T02:55:00 | 2020-02-01T03:17:00 |
  | 2020-02-01T03:27:00 | 2020-02-01T04:12:00 |
  | 2020-02-01T04:20:00 | 2020-02-01T04:29:00 |
  | 2020-02-01T05:19:00 | 2020-02-01T05:23:00 |
  </code></pre>
  
  <pre><code>df2
  
  | Time                | Percent |
  |---------------------|---------|
  | 2020-02-01T00:00:00 | 1       |
  | 2020-02-01T00:01:00 | 1       |
  | 2020-02-01T00:02:00 | 0.750   |
  | 2020-02-01T00:03:00 | 0.833   |
  | 2020-02-01T00:04:00 | 0.350   |
  | 2020-02-01T00:05:00 | 0.066   |
  </code></pre>