All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
We do not know of any sound evidence from the Quran or the Sunnah that supplication is accepted when said at seeing the Ka'bah for the first time or any other time.
Al-Bayhaqi and At-Tabaraani reported that the Prophet said: "The gates of heaven are opened and supplication is accepted in four situations: at the time the rows meet for the sake of Allaah (meeting the enemy in Jihaad), when it is raining, at the time of Iqamaah of the prayer, and at the time the person sees the Ka'bah." However, this narration was graded by Al-Albaani as 'very weak' and Ibn Hajar said that 'its chain of narrators was weak.'
Allaah Knows best.