A couple of years ago, I heard this piece performed, and then didn't rest until I'd hunted down a copy of it.
The only one I could find was the rather fancy "Limited Edition" printed by Breitkopf & Härtel in 2002 - pretty green hardcover, gold lettering, the works - which came with an introduction. Part of that is the following:
"Even if "Wie die Zeit läuft!" (How time flies!) is not officially designated as a "song without words", this appellation, created by Mendelssohn himself, could most certainly be applied to describe the genre of this little piece.
Mendelssohn had a lifelong interest in the transitoriness of time. In his correspondence, one often encounters passages that celebrate a happy past but look to the future as a time of darkness. Mendelssohn basked in the memory of his carefree past and often perceived the present and future as oppressive, partly because of his enormous workload. This musical miniature also radiates a feeling of melancholy."
-- Leipzig 2001, Patrick Kast, Christiane Schmidt
In short - a song without words which isn't a song without words. It is, however, a joy to play and well on its way of becoming my new favorite encore.
Performed 16-11-2014 at the Central Library, The Hague