The WhatsApp 24-hour window: what it is and how not to lose the conversation

The 24-hour window is the period in which a business can reply freely on WhatsApp, with any message type, after the customer writes. It is the rule that organises everything on the official API: it decides what can be sent, when, and what Meta charges for.

What opens and closes the window

Opens: any message the customer sends to the business number. From that moment, 24 hours start counting.

Restarts: every new customer message. If they answer three hours later, the clock goes back to zero.

Does not open or extend: messages the business sends. A delivered template opens no window — only the customer's reply to it does.

Closes: silence. After 24 hours with no customer message, free-form conversation ends.

What changes inside and outside the window

	Inside the window	Outside the window
Message types	text, image, audio, document, buttons	only an approved template
Charged by Meta	not charged	per message, by category
Who can send	team and agents	team and agents, with a template

That is why response speed becomes a cost metric, not just a courtesy: replying inside the window is free; letting it expire means paying for a template to get back in.

The 72-hour window

There is one important exception. Conversations that start from a free entry point — a click-to-WhatsApp ad or a button on a Facebook page — open a 72-hour window, and messages inside it are not charged by Meta. It is a direct incentive to bring customers in through the ad path instead of blasting cold templates.

What to do when the window expires

1. Send a utility template when there is a concrete fact to communicate — order, booking, status. It reopens the conversation and costs little.
2. Do not push marketing to reopen a pending support thread: it is more expensive and it is exactly the kind of message that draws reports.
3. Ask for the reply. A template with a quick-reply button lets the customer reopen the window with one tap — and from there the conversation is free again.

How this looks in practice

In the Nivox inbox every conversation shows the time left on the window, and the same state applies to AI agents: outside the window, a free-form send is refused by the server, not by the agent's good judgement. That is the difference between a rule written in a prompt and a rule that cannot be talked around.