In "Horyakukanki" (a history book of 14th century Japan), it is written that 'Taira no Dainagon Tokitada is the younger brother of Kita no kata, Niidono (the second ranked), of the dajonyudo (prime minister who became a priest))' and, therefore, it seems sure that Tokitada was the younger brother of Tokiko.
『保暦間記』にも「平大納言時忠ト申ハ、太政入道ノ北方二位殿ノ弟也」とあり、時忠が時子の弟であることは間違いないと思われる。