title: ValueError: time data does not match format '%HH:%MM:%SS' when subtracting two time strings
body: <p>I am trying to find the difference between two time strings with the following python code.</p>
  
  <pre><code>print('time base one {}'.format(time_base_day_one))
  s1 = '24:00:00'
  s2 = time_base_day_one
  FMT = '%HH:%MM:%SS'
  
  print('type of time_base_day_one {} type of s1 {}'.format(type(time_base_day_one),type(s1)))
  time_offset_day_two = datetime.strptime(s2, FMT) - datetime.strptime(s1, FMT)
  </code></pre>
  
  <p>I am getting the following error.</p>
  
  <pre><code>ValueError: time data '11:00:19' does not match format '%HH:%MM:%SS'
  </code></pre>