Short answer. You must fulfill it as soon as you learn of the testator's death. Article 876 of the Civil Code provides that any purely potestative condition imposed on an heir must be fulfilled by that heir as soon as they learn of the death. There is no extended period to wait and see.
What the law says
Any purely potestative condition imposed upon an heir must be fulfilled by him as soon as he learns of the testator's death. This rule shall not apply when the condition, already complied with, cannot be fulfilled again.
Civil Code, Article 876 — Purely Potestative Conditions. Read the full provision →
What a purely potestative condition is
A purely potestative condition is one that depends entirely on the will of the person upon whom it is imposed — not on external events, chance, or the actions of others. In the context of succession, a testator may attach a condition to a bequest or inheritance that the heir must personally perform some act, such as visiting a family grave, pursuing a particular study, or some other act that lies entirely within the heir's power to do or not do. Article 876 of the Civil Code governs exactly when such a condition must be fulfilled.
The deadline: as soon as you learn of the death
Article 876 is explicit about timing: Any purely potestative condition imposed upon an heir must be fulfilled by him as soon as he learns of the testator's death. The trigger is not the settlement of the estate, not the formal probate of the will, and not some other administrative milestone — it is the moment the heir learns that the testator has died. From that moment, the heir is expected to act on the condition without delay. Because the condition is something entirely within the heir's power, the law does not grant an extended waiting period.
The exception: conditions already performed that cannot be repeated
Article 876 contains a sensible exception: This rule shall not apply when the condition, already complied with, cannot be fulfilled again. If the condition is one that the heir has already satisfied before the testator died — such as completing a particular degree or achieving some milestone — and it is the kind of act that cannot be done again, the heir is not expected to re-do something they have already done. The condition is treated as already fulfilled. This prevents the absurd result of asking an heir to accomplish something that has become impossible because it already happened.
Consequences of not fulfilling the condition on time
Because a purely potestative condition depends entirely on the heir's own will, the heir who learns of the testator's death and then delays or refuses to fulfill the condition is essentially choosing not to comply. Article 876's requirement that the condition be fulfilled as soon as the heir learns of the death reflects the testator's intent that the condition be met promptly. Whether failure to fulfill the condition promptly results in the inheritance lapsing or some other consequence depends on how the testator framed the condition in the will. The nature and specific terms of the condition, as expressed in the will, control what happens if it is not timely fulfilled.