I think at least a year. Probably easier for you in the UK, where it is damp. Hard to grow feather and keep it, here in the desert, SW of the US.
Once it is grown, make absolutely sure, you check under it, right down to the skin, once a week. Watch for signs of stamping, biting at feet while standing or lying down and/or rubbing the back of feet and pasterns, on anything handy. Look here for info as to why I say this... Chronic Progressive Lymphedema
PS. Pictures are a must! On this forum, if you don't show us pics, then most of us don't believe the animal exists.