'Set the time stamp for when the certificate starts being valid
:param when: A string giving the timestamp, in the format:
YYYYMMDDhhmmssZ
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
:type when: :py:class:`bytes`
:return: None'

def set_notBefore(self, when):

    return self._set_boundary_time(_lib.X509_get_notBefore, when)
