The Torah commands in Parashat Re’eh (Debarim 12:5-6), “You shall come there, and you shall bring there your burnt-offerings…and your pledges…” These verses establish an obligation to fulfill one’s pledges to the Bet Ha’mikdash by the first Regel (pilgrimage festival) that is celebrated after making the pledge. If a person commits to offer a voluntary sacrifice, or to make a donation to Bedek Ha’bayit (the treasury of the Bet Ha’mikdash), he has until the soonest Regel to fulfill this pledge. This Halacha is inferred from the word “Shama” (“there”), which implies that the sacrifice or donation must be brought immediately when you arrive “there” in the Bet Ha’mikdash, meaning, the first holiday requiring a pilgrimage to the Bet Ha’mikdash, when one comes to the holy site. At that first opportunity, he must fulfill his pledge. The reason for this Misva, of course, is that one should not be lazy or apathetic toward his commitments to the Bet Ha’mikdash. Just as people are careful to fulfill their civic duties in timely fashion, we must similarly ensure to fulfill our obligations to the Bet Ha’mikdash without delay. Nevertheless, the Torah does not require one to fulfill his pledges immediately, as this would pose an unreasonably difficult burden, and would discourage people from pledging to offer sacrifices and to donate to the Temple treasury. In addition to this affirmative command, there is a separate prohibition – known as “Bal Te’aher” – which forbids delaying the fulfillment of one’s pledges to the Bet Ha’mikdash. That prohibition is not violated until three Regalim pass before one fulfills his pledge. As mentioned, the affirmative command to fulfill one’s pledge requires bringing the sacrifice or donation before the end of the first Regel that is observed after one makes the pledge. This Misva applies in the times of the Bet Ha’mikdash. Nowadays, when, unfortunately, we do not have a Bet Ha’mikdash and are thus unable to bring sacrifices, one who pledges to offer a sacrifice clearly is not bound by this Misva.