You can customize the way timestamps display to commenters on both the comment stream and their My Profile tab. The default display is via relative timestamps, e.g. "2 minutes ago", "20 days ago", "3 months ago".
Customizing this will require creating a plugin that leverages the two plugin slots commentTimestamp and historyCommentTimestamp to replace this with a custom component.
For more information, please see https://github.com/coralproject/talk/pull/979.