Depends on the tension of the restraints and or clamps etc, also position of torso etc. But medically speaking I think you should consider relaxing tension on very tight bindings etc for a short period about every 10 minutes (or less if real pain sets in).

I would not recommend anyone try to maintain a fixed and restrained position for as long as half hour at a time. Long term health problems can creep up unnoticed so care is needed in your games.