To access the session timeout parameter, you could create an OutSystems extension with an action that accesses the HTTP Session context of the executing HHTP request. You can then reference this action in you eSpace in Service Studio.
In case we are talking about the OutSystems .Net stack, you could use the ASP.Net Session.Timeout parameter of the current session. I have not tried it myseld, but it would be something like HttpContext.Current.Session.Timeout . You just have to create and extension action that returns this value.
I hope this helps,