sed -i 's/auth.generate_token",\[300/auth.generate_token",\[129600/g'  /usr/share/truenas/webui/*.js

sed -ie 's/auth.generate_token",\[300/auth.generate_token",\[129600/g' /usr/local/www/webui/*.js

Source: Extend TrueNAS Web UI Session Timeout | Tom Schlick