code: def time_to_first_byte(self):
          
          # The unknown page is just a placeholder for entries with no page ID.
          # As such, it would not have a TTFB
          if self.page_id == 'unknown':
              return None
          ttfb = 0
          for entry in self.entries:
              if entry['response']['status'] == 200:
                  for k, v in iteritems(entry['timings']):
                      if k != 'receive':
                          if v > 0:
                              ttfb += v
                  break
              else:
                  ttfb += entry['time']
  
          return ttfb
docs: Time to first byte of the page request in ms