def get_session_not_on_or_after(self):
        """
        Gets the SessionNotOnOrAfter from the AuthnStatement
        Could be used to set the local session expiration

        :returns: The SessionNotOnOrAfter value
        :rtype: time|None
        """
        not_on_or_after = None
        authn_statement_nodes = self.__query_assertion('/saml:AuthnStatement[@SessionNotOnOrAfter]')
        if authn_statement_nodes:
            not_on_or_after = OneLogin_Saml2_Utils.parse_SAML_to_time(authn_statement_nodes[0].get('SessionNotOnOrAfter'))
        return not_on_or_after
Gets the SessionNotOnOrAfter from the AuthnStatement
        Could be used to set the local session expiration

        :returns: The SessionNotOnOrAfter value
        :rtype: time|None