docs: def timestamp(stamp, tolerance=150):
      """Validate timestamp specified by request.
  
      See `validate.request` for additional info.
  
      Args:
          stamp: str. Time request was made as ISO 8601 timestamp.
          tolerance: int. Number of seconds request remains valid from timestamp.
  
      Returns
          bool: True if valid, False otherwise.
      """
      try:
          tolerance = datetime.timedelta(0, tolerance)
          timestamp_low = dateutil.parser.parse(stamp)
          timestamp_high = timestamp_low + tolerance
          now = datetime.datetime.now(timestamp_low.tzinfo)
      except ValueError:
          return False
  
      return now >= timestamp_low and now <= timestamp_high