At least in a backhanded way, ISO 9001 does provide some guidance on calibration intervals. It may not seem evident though.
I think that it goes without saying that you don't want to do it so often that it is burdensome.
The outer limit is from the paragraph in 7.6 right below the letters (7.6 a-e) where it states:
"In addition, the organization shall assess and record the validity of the previous results when the equipment is found not to conform to requirements. The organization shall take appropriate action on the equipment and any product affected."
Determining and taking appropriate action on the equipment may not be very difficult, but doing so on the product affected can be a huge liability and a huge project as well, one that you don't want to do if at all possible. This, in my mind is the outer side of the interval. It needs to be often enough that your risk is mitigated as much as practical.
Simply choosing an interval of two years without thinking through the impact could expose you to a lot of risk.