I had a dog that had two done. It was a while ago, but to the best of my recollection we did them approximately one year apart. At the time we had the first one done, we knew that the other would have to be done as well. We did the worst one first, rehabbed it and gave the dog some time, and then did the other. I don't know if there is a typical time and don't recall any specific recommendation from the vet on this. Our decisions were driven based on the dog's condition and quality of life.