This is splitting hairs - had a discussion with a German speaking friend and there its translated to something like use or make the most out of the day.
The canonical German translation is "pflücke den Tag", which is exactly "pluck the day", as suggested in the article.
German here. Never heard that translation. Could be either regional or an old translation. Here, we would say "Nutze den Tag" -- "make use of the day" in the sense of "don't waste it".