The suggestion I see online and that my doctors have mentioned is 3-5 years. I don't know what happens if you take a break after that time, whether you can take it again, and what the ideal break from it is. I would think the effects would be cumulative but I am not sure that the optimal duration has been confirmed by research.

I found this: on https://www.rxlist.com/reclast-drug.htm#dosage
Important Limitations Of Use
The safety and effectiveness of Reclast for the treatment of osteoporosis is based on clinical data of three years duration. The optimal duration of use has not been determined. All patients on bisphosphonate therapy should have the need for continued therapy re-evaluated on a periodic basis. Patients at low-risk for fracture should be considered for drug discontinuation after 3 to 5 years of use. Patients who discontinue therapy should have their risk for fracture re-evaluated periodically.

This article gave a little different picture but is from 2016
https://www.health.harvard.edu/newsletter_article/how-long-should-you-take-a-bisphosphonate-for-osteoporosis

Basically I don't think there is a definite answer and like everyhing it depends on the individual. Atypical femur fracture and jaw necrosis are the risks. The big question I think is whether risk is cumulative, with different courses with a break in between. Or does a drug holiday reduce risk so that more can be given?