It can take around three years for breasts to fully develop from starting HRT. You may want to wait until your breasts have developed as much as can naturally before considering breast augmentation surgery.
You will also need to have enough skin for the implant to sit under. If you have a very taut, 'masculine' chest with less available skin then it can be difficult to fit the implant under it. If you have more skin / soft tissue then it will be easier to fit implants.
You can find more information on the timescales of HRT on our website.