No we absolutely, positively do not need to have two keys -- the inferred meaning is "ago" because that's the only thing that date next to the post could possibly mean.
Should we also print USER: next to the gravatar on each post so that people do not get confused that the avatar to the left of the post is the user who composed the post? Because I might get confused! There's just this avatar floating there next to the post, what could it possibly mean! I don't get it, can someone explain to me what that avatar means next to the post?
Oh, the user who created the post. Well, why don't we print USER: next to it, to make that clear, so there is no possibility for confusion.
Because it's obvious and redundant and unnecessary? Exactly my point.
If a particular language combines "minutes ago" into a single word, without saying "ago", that just means the language is superior to English in this regard. The correct translation is equivalent as-is. To make it 100% clear:
is the same as
where ☃ means "minutes ago".