According to Official Guinness Records,
The longest beach volleyball marathon lasted 25 hr 39 min achieved by Mateusz Baca, Sebastian Lüdke, Tomasz Olszak, and Wojciech Kurczynski (all Germany) in Görlitz, Germany, on 3-4 July 2010. The attempt was made at the Rosenhof sports and leisure centre by the four members of sports club VfB Görlitz.
The attempt began at 9:01:32 a.m. on 3 July and ended at 10:41 a.m. on 4 July.
For a complete list of 2010 records, please visit 2010 Guinness Records in Germany.