Update 01. Chats.md

added explanation for session window, and flow getting killed

docs/3. Product Features/01. Chats.md

@@ -62,3 +62,11 @@ A green phone-like icon towards the right bottom end is present which acts as a
 
 <img width="281" alt="Screenshot 2024-02-29 at 12 13 21 PM" src="https://github.com/glific/docs/assets/143380171/0bbf03af-1c81-4af3-a834-b0719d7b7d93"/>
 
+**For contacts who stop responding to the chatbot**
+
+The contact remains in the “session window” for 24 hours after the last message is sent by the contact. This means that, for the 24 hours period, any free flowing message can be sent to the contact from the chat window. 
+
+Once the contact is out of "session window" indicated by `0` next to their chat name. The only way to send the contact a message is by using HSM templates.
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+The contact remains in the flow for 5 days after the last message is sent, this means that responding to a message within 5 days, will take the conversation forward within the flow. However after 5 days, the flow is “killed” and any response to a question within the flow is not recorded within the flow. 
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