Hi konijn,
Im not sure about the whole after work thing. I do know that there is a free beach volleyball court at oberer letten which is close to limmatplatz in Zurich.
http://map.search.ch/d/tc0owixmm
I would definatly be up for playing once if you have a ball and we can get some more players.
It is busy so im not sure when the best time to go is?