No, there is no timeout in FOP2 itself. However, FOP2 will kick unresponsive clients.. an unresponsive client is a browser that is not sending keepalives (and by default, all fop2 connected clients will send a keepalive packet every few seconds).
You can start FOP2 in debug mode and look at the log at around the time a user gets disconnected, and you might see some lines indicating the reason for the disconnection, it could also be a kind of socket error/network disconnection.
http://members.asternic.biz/knowledge_base/how-to-debug-fop2
