Every inbound user message opens or resets the window, so an active back-and-forth conversation can stay open indefinitely — the clock restarts each time the customer writes.
Inside the window. The business can send anything the platform supports: text, images, documents, interactive buttons, product cards. These service replies are not billed by Meta and do not count against messaging limits, which makes the open window the cheapest and most flexible place to operate. It is also where chatbots and AI agents deliver most of their value, resolving questions in real time while the conversation is free.
Outside the window. Once 24 hours pass without a new user message, free-form sending is blocked at the API level. To re-engage, the business must send an approved template message — a marketing, utility, or authentication template billed per delivered message. A template that prompts a reply reopens the window and returns the conversation to free-form mode.
Design implication. Well-built WhatsApp programs are engineered to keep users talking: fast responses, questions that invite replies, and template nudges timed to reopen dormant threads.
Why it matters for brands
The window defines both cost and compliance on WhatsApp. Answering while it is open costs nothing; letting it lapse means paying template rates and passing Meta review to say anything at all. Response speed is therefore a direct margin lever.