Ilizarov's classic average indicative value tested for 40 years was, for totally complying, young, healthy patients, twice the time of elongation, meaning 80 x 2 = 160 days for 8 cm. But this varies depending on a lot of things: walking early with crutches, active mobilization (in the proper time) and cooperation of patient with physiotherapists, not rimming too much medullary tissue, preservation of periostium, proper insertion of wires by an experienced surgeon, never raise normal previous distraction velocity for elongation (1mm / day divided in the shortest fractions as possible, ideally continously with an "engine") except in due fully justified cases, etc.
It also depends on age of patient, own biology/ genetics of patient, food, supplements and possible medication, contraction for shorter periods before restart of elongation if consolidation difficult, initial stature and state of bone tissue, individual flexibility of tendons and muscles, etc.
To sum up, it's not possible to forecast exactly.
