def gmtime_adj_notAfter(self, amount):
if not isinstance(amount, int):<EOL><INDENT>raise TypeError("<STR_LIT>")<EOL><DEDENT>notAfter = _lib.X509_get_notAfter(self._x509)<EOL>_lib.X509_gmtime_adj(notAfter, amount)<EOL>
Adjust the time stamp on which the certificate stops being valid.

:param int amount: The number of seconds by which to adjust the
    timestamp.
:return: ``None``