You need to get the time of the first message and the last verb time of the last message in the thread. Or get the date from the sent folder. Getting the last message is harder if you want it fully automatic with a macro.
If you want to do it in Excel, you can use the cfg here to get the replied to time - then create a view with the field you want and copy and paste into Excel.
How to show the sender’s e-mail address and other fields in a column in message list view using custom fields.
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