Fixed setting backoff-expires

Previously was adding `parsed_result[backoff]` to a datetime object. The key to `parsed_result` is the *string* 'backoff', and the value is an integer (in seconds). It is therefore necessary to convert this using `datetime.timedelta`.

In addition to this, some of the demos added `..` to `sys.path` whilst others did not &ndash; I have added this to all of them for consistency.