Around a year, I stopped being able to feel the breast bud under the nipple unless I pressed on it. Around two years, it disappeared completely. By three years or so, the entire breast had softened somewhat (the firmness is new breast tissue, but fat will be layered on top of that, and gradually that fat will give it the soft squishiness of a mature breast).
I'm now coming up on 5 years HRT and 42DDD, still growing very slowly but it's all fat depositing now.