I’m not sure it’s possible to disable the auto logout within the WebUI services.
You may need to submit a PMR to IBM to see if a setting even exists to do this. I did a quick Google search for “bigfix” and “_WebUIApp”, but not finding anything.
Alternatively, you could use a dashboarding tool like IBM Dash or an open source alternative that updates queries for the desired dashboard on a schedule via the BigFix REST API.