Short answer. It retroacts to the death. Article 1042 provides that the effects of accepting or repudiating an inheritance always go back to the moment the decedent died, not the later date you actually accept or refuse. Legally, you are treated as heir, or as never having been heir, from that earlier moment.
What the law says
The effects of the acceptance or repudiation shall always retroact to the moment of the death of the decedent.
Civil Code, Article 1042 — The Effects Retroact to Death. Read the full provision →
The law backdates your decision to the death
Article 1042 is short but decisive: The effects of the acceptance or repudiation shall always retroact to the moment of the death of the decedent. Whether you accept or repudiate an inheritance days, months, or years after your relative dies, the law does not treat the interval as a gap where nobody held the estate. Your decision is given legal effect as of the exact moment of death, so there is no period during which the succession is left in limbo simply because you had not yet decided or announced anything.
What retroactivity means if you accept
If you accept, you are considered to have been the owner of your share from the instant your relative died, not merely from the day you signed an acceptance or otherwise made your intention known. Any fruits, rents, or increases the inherited property produced in the meantime are generally treated as yours from that earlier date as well, because the law is not creating a new right on the day of acceptance; it is simply confirming, after the fact, a right that had already vested at death.
What retroactivity means if you repudiate
If instead you repudiate, the retroactive effect works the other way: you are treated as if you had never been an heir at all, from the moment of death onward. Whatever share would have passed to you is regarded, from that same starting point, as having gone to whoever is entitled to it in your place, whether by accretion among the other heirs or by substitution or representation. There is no in-between stage where you were briefly an heir before dropping out; the law simply erases you from that line of succession as of death.
Why the law fixes the moment at death
Succession itself opens at the moment of death, and property, rights, and obligations of the deceased need a single, fixed point from which everyone's status can be measured. Letting the effective date float depending on when each heir happened to decide would leave ownership uncertain for however long deliberation took, and would complicate anything that occurred with the estate in the meantime. Anchoring both acceptance and repudiation to the date of death gives every interested party, and anyone dealing with the estate, one consistent reference point.