Hi @NP
According to our tests, the full format of the date can only be displayed in chat history.
In the chat list, non-today's dates will show only the date (no time), and today's chats will show the time.
This is by design, to get this feature more quickly, you can send a feedback directly to Microsoft Feedback to add it in future updates.
Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future.
Thanks for your understanding and support.
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