Yes! I made a similar suggestion on HN, though like your labels better. I was thinking a bit more on it that after "just now" and a hypothetical "new" that the timestamp could disappear so long as there has been a response within X amount of time, for example, after 2 months. After this time period it could start saying things like, "a while ago," "quite a while ago," and "a long time ago" based on (for example) 1 years ago, 2 years ago, > 2 years ago.