Short answer. At the moment the decedent dies. Article 1034 says an heir, devisee, or legatee's capacity to inherit is judged by their qualification at the time of the decedent's death. Some situations require waiting, for certain unworthiness grounds until a final judgment, and for a conditional gift the time the condition is fulfilled is also considered.
What the law says
his qualification at the time of the death of the decedent shall be the criterion
Civil Code, Article 1034 — When Capacity Is Judged. Read the full provision →
Death fixes the baseline
Succession opens at the moment a person dies, and that instant is the reference point for deciding who may inherit. Article 1034 provides that in order to judge the capacity of an heir, devisee, or legatee, his qualification at the time of the death of the decedent shall be the criterion. What matters is the potential heir's standing on the date of death, not months earlier or later. Someone qualified then is in a position to inherit; someone disqualified then generally cannot cure the defect afterward, and the transmission of rights is measured from that moment.
When you must wait for a final judgment
For some grounds of unworthiness the answer cannot be settled at the instant of death, because they turn on facts that a court still has to establish. In those cases the law requires waiting until a final judgment is rendered before the heir's capacity is treated as fixed. Until the matter is finally decided, the question of whether the person is disqualified stays open. The criterion is still tied to the situation at the decedent's death, but its legal confirmation waits on the outcome of the proceeding.
Conditional gifts and the time of compliance
A gift can also be made to depend on a condition, and that changes when capacity is assessed. Article 1034 adds that if the institution, devise, or legacy is conditional, the time of compliance with the condition is likewise considered. So beyond being qualified at the decedent's death, a conditional beneficiary must also satisfy the condition, and the moment that condition is met is part of the picture. Both points in time can matter for a beneficiary whose gift is not outright.
Why timing is decisive
Pinning capacity to the death of the decedent, with these adjustments, gives succession a clear and stable starting line. It prevents disputes from turning on shifting circumstances after death and lets the estate be settled on a known set of facts. For anyone assessing whether a particular person may inherit, the first question is always their standing at the moment the decedent died, with an eye to any pending unworthiness proceeding or unfulfilled condition that the law says must also be weighed.