The runtime doesn't timeout webservice calls. However, in most production environments you will probably run a mendix runtime behind a frontfacing webserver such as nginx or apache. It is quite possible (and common) for these front-facing webservers to have a timeout. You'll have to contact your system administrator if you'd like to change that setting.
AFAIK by default there is no timeout. The connection will run forever until the connection is closed or some intermediate host drops it.
See this thread