v6.9.0-rc2.
Configuration of how dates and times appear is spread over multiple Settings > User Preferences. Display Settings has one kind of date configuration, and then Notification Settings has another. And I don't even think that they're the same; Notifications had DD-MM-YYYY.
Please consider putting all date/time options in the Settings > System Settings > Date and Time option, and collapse to a single standard. If I select YYYY-MM-DD, I wouldn't expect that I'd see that format in one place, but a different format in another. (Notification popup vs. a log message for example).