Short answer. From the moment the acceptance is communicated to your agent. Article 1322 provides that an offer made through an agent is accepted from the time acceptance is communicated to him, not from when it later reaches you personally, so the effective moment is your agent's receipt, not yours.
What the law says
An offer made through an agent is accepted from the time acceptance is communicated to him.
Civil Code, Article 1322 — Offer Through an Agent. Read the full provision →
The agent's receipt is what counts
Article 1322 fixes a clear, single moment for when a contract offered through an agent becomes accepted. It states that an offer made through an agent is accepted from the time acceptance is communicated to him. Because you made your offer through an agent, the acceptance takes effect as soon as the other party communicates it to that agent, not at some later point when the agent gets around to relaying the news to you personally. The agent's receipt of the acceptance is treated as legally equivalent to your own.
Why the law treats the agent's knowledge as your own
An agent acts on your behalf specifically to handle this kind of communication, and requiring the other party to wait until the acceptance actually reaches you, the principal, personally, would undercut the entire purpose of using an agent to conduct the negotiation. Treating communication to your agent as communication to you keeps the timeline predictable for both sides and avoids disputes over whether or when the acceptance eventually made its way from the agent to the principal.
What this means for calculating the contract's timeline
Any consequence that depends on the moment of acceptance, such as when the contract is perfected or when related deadlines begin to run, should be measured from when your agent actually received the communication of acceptance, not from any later date you personally learned about it. If there is a gap between when your agent was told and when your agent informed you, that gap does not delay the legal effect of the acceptance itself.
What this means practically for using an agent
Because the acceptance becomes effective at your agent's end, it matters that your agent promptly and accurately communicates what was received to you, since you may be legally bound to a contract from that earlier moment even before you personally find out. Choosing a reliable agent, and setting clear expectations about prompt reporting, protects you from being caught off guard by an acceptance that already took legal effect. It also means you should treat any delay between your agent hearing the acceptance and telling you about it as your own risk to manage, not a gap the law will bridge in your favor.