Actually, there have been a number of other M3/VI movements that are less than 21 minutes in length: Solti (both times), Neumann I, Barbirolli/Halle (yes, Barbirolli), Horenstein (Turin, 1960), Kondrashin, Leinsdorf, Bruno Maderna, Mitropolous (both times), Scherchen (Vienna, 1950), Schuricht, Hans Vonk, Tennstedt (LPO, 1979) - all well less than 21 minutes in duration.