Praise be to Allaah.
With regard to the obligatory Hajj, one should hasten to do it, because the Prophet (peace and blessings of Allaah be upon him) said: “Hasten to do Hajj, for no one of you knows what will happen to him.” And ‘Umar ibn al-Khattaab (may Allaah be pleased with him) said, “Whoever dies without having done Hajj when he had the means to do so, he might as well die as a Jew or as a Christian.”
With regard to supererogatory (naafil) Hajj or ‘Umrah, a person can change his mind, and he does not sin by doing so, so long as he has not started the rituals, because Allaah says (interpretation of the meaning):
“And perform properly (i.e. all the ceremonies according to the ways of Prophet Muhammad), the Hajj and ‘Umrah (i.e. the pilgrimage to Makkah) for Allaah” [al-Baqarah 2:196]
He may choose the time that suits him; even if he has resolved to travel (for that purpose) then changes his mind, there is nothing wrong with that.