Hi Martin,
That setting is here I think
frappe@ubuntu:~/frappe-bench$ grep gunicorn config/supervisor.conf
command=/home/frappe/frappe-bench/env/bin/gunicorn -b 127.0.0.1:8000 -w 1 -t 120 frappe.app:application --preload
This docs gunicorn timeout Settings — Gunicorn 21.2.0 documentation
Here trentmu notes a timeout from say a circular reference in a BOM tree Worker timeout (Stock Entry/transfer on Production Orders)