The "WhatsApp 24-hour Customer Care Window" is a 24-hour time frame during which a company can freely respond to an incoming message.
By "freely," we mean a message that can be fully typed by the company. Outside the 24-hour Customer Care Window (24H CCW), a WhatsApp template message must be used.
WhatsApp created this to maintain the quality of conversations held on their platform and to ensure a quick response time.
The 24H CCW is extended by 24 hours each time the relevant contact sends a message. This means that a ongoing conversation where the company can freely respond can last longer than 24 hours until the request from the person with whom the conversation is being held is completed.
Saysimple indicates when the 24H CCW is closed through a notification above the text field"
And with a 'bell'-icon: 🔔 in the conversations list: