The desktop-timeout Element
From Documentation
Syntax:
<desktop-timeout>a_number</desktop-timeout>
[Default: 3600]
It specifies the time, in seconds, between client requests before a desktop is invalidated. A negative time indicates the desktop should never timeout.
In 9.x and before, it only works when the current desktop count exceeds max-desktops-per-session
and while adding a new desktop (both conditions should match).
Since 10.0.0 It works regardless of the current desktop count.