The "classic" old advice when folks drove 10,000 miles a year was to check the torque as a part of your annual tune-up which was nominally 10,000 miles.
My advice, after a head gasket change, retorque after about 30-45 minutes of running, again after 5-15 hours of running, and again at the end of the first season.
Thereafter, I would continue to check it annually until such time that the applied torque is no longer resulting in any tightening of the fasteners, i.e. you've reached a stable steady state condition.