docs: def day_interval(year, month, day, milliseconds=False, return_string=False):
      """
      Return a start datetime and end datetime of a day.
  
      :param milliseconds: Minimum time resolution.
      :param return_string: If you want string instead of datetime, set True
  
      Usage Example::
  
          >>> start, end = rolex.day_interval(2014, 6, 17)
          >>> start
          datetime(2014, 6, 17, 0, 0, 0)
  
          >>> end
          datetime(2014, 6, 17, 23, 59, 59)
      """
      if milliseconds:  # pragma: no cover
          delta = timedelta(milliseconds=1)
      else:
          delta = timedelta(seconds=1)
  
      start = datetime(year, month, day)
      end = datetime(year, month, day) + timedelta(days=1) - delta
  
      if not return_string:
          return start, end
      else:
          return str(start), str(end)