I'm writing this here since I'm going to want to do it some point in the future and this info is incredibly hard to find. 
If you back up your iPhone to your Mac, you will find in that backup an unencrypted SQLite file that is your message DB.
The iOS backup is located at: /Users/victor/Library/Application Support/MobileSync/Backup/
Within the folder of your specific backup, you can find the message file here: 3d/3d3d0d7e5fb2ce288813306e4d4636395e047a3d28
The most interesting table is the message table and to convert a date to a reasonable value you can do:
DateTime.from('2001-01-01').plus({seconds: date / 1_000_000_000})

I'm writing this here since I'm going to want to do it some point in the future and this info is incredibly hard to find. 

If you back up your iPhone to your Mac, you will find in that backup an unencrypted SQLite file that is your message DB.

/Users/victor/Library/Application Support/MobileSync/Backup/

Within the folder of your specific backup, you can find the message file here: 

3d/3d3d0d7e5fb2ce288813306e4d4636395e047a3d28

 table and to convert a date to a reasonable value you can do:

DateTime.from('2001-01-01').plus({seconds: date / 1_000_000_000})

How to Extract iOS Messages from your iOS Backup