NRC: Recommended practices for calibration laboratories:

https://nrc.canada.ca/en/certifications-evaluations-standards/calibration-laboratory-assessment-service/recommended-practices-calibration-laboratories

Intervals of calibration

Test equipment and measurement standards should be calibrated at periodic intervals established and maintained to assure acceptable measurement uncertainty and reliability. Intervals should be shortened or may be lengthened when the results of previous calibrations indicate such action is necessary or sufficient to maintain acceptable reliability. ISO 10012-1 Annex A and NCSLI RP-1 Establishment and Adjustment of Calibration Intervals contain guidelines for the determination of calibration intervals for measuring equipment.

Reliability means the probability of equipment remaining in tolerance during the calibration interval, and for standards, the probability of the assigned value of the standard not changing by more than the list of uncertainties. In the client's laboratory, the list of uncertainties should include any uncertainty associated with drift rate. The procedure for assigning calibration intervals and adjusting them should be fully documented. The laboratory should have a fully-documented recall system for all its test equipment and standards to assure timely recalibrations. The recall system may allow temporary extension of the calibration due date for limited periods of time under specific conditions such as the completion of a test in progress.

NRC: Discussion on calibration intervals:

https://nrc.canada.ca/en/certifications-evaluations-standards/calibration-laboratory-assessment-service/discussion-calibration-intervals

Definitions

Calibration Interval

Period of time or amount of use between calibrations
To ensure equipment remains reliable

Reliable

Within sufficient tolerance (or uncertainty) for the tests being done