I'm using biotin, mainly for the hair and for it's qualities for improving skin and nails. I'm using it well above recommended doses, as there is no harm from overdose as it just doesn't get absorbed.
For hair it takes so long to see any results and I have been using it just for two months and I have a long hair, so I think that for my hair it takes a year or more to see the results.
However, I can definitely tell that the hair grow in rest of the body has increased significantly, which kind of sucks. But why I continue using it, is that my eyelashes have grown! Especially the lower eyelashes are now long ones and getting more thicker.