Ruling on vows. Fulfilling legitimate (shar’i) vows is obligatory according to sharee’ah. Allaah says (interpretation of the meaning): “Then let them complete the prescribed duties (manaasik of Hajj) for them, and perform their vows…” [al-Hajj 22:29]. Imaam al-Shawkaani said: “This means that they have to do this.”
This vow comes under the heading of vows to do acts of worship and obedience, so it must be fulfilled, whether it was general or conditional. A general vow is when a person says, for example, “I vow – or I promise to Allaah – that I will sacrifice a sheep, or give it to the poor or to my relatives.”
A conditional vow is one where a person says, for example, “If Allaah heals me, or if I succeed, or I get a salary, or I acquire such and such an amount of money, I will offer a sacrifice etc.”
With regard to the obligation of fulfilling the vow, that is because the Prophet (peace and blessings of Allaah be upon him) said: “Whoever vows to obey Allaah, let him obey Him, but whoever vows to disobey Allaah, let him not disobey Him.” Narrated by al-Bukhaari (6318).
So long as you did not stipulate a specific time for fulfilling your vow, then it is permissible for you to fulfil it at any time, during the days of Eid al-Adha or at any other time.
But if you intended to offer a sacrifice this year, the sacrifice in fulfilment of your vow does not count as the udhiyah sacrifice too, even if it is sacrificed during the days of Eid al-Adha.