Nobody can really answer those questions. If you are starting to clearing then it shouldn't take long, although some people on antibiotics never reach completely clear face. As for how long will it stay clear - if you use it long enough you will be eventually resistant to it. Well not you but bacteria in you of course. When it comes it will not longer work for you, but often it takes really long time to get resistant to monocycline. So long that is really not a good idea for a different reasons(effect of antibiotic on your gut and possible other side effects like drug-induced lupus in case of minocycline). It should work on cystic acne too, but only when you are on it. You have to find something else when you are on oral antibiotic to use on your face when you are done with it.

I used mino 100 mg with differin 0.1 creme, worked wonders for me, I had REALLY wonderful skin (it took me 2-3 months). The bad thing is, it came all back after 4-5 months, it makes me really depressed! That's why antibiotics are actually not a solution... I don't wanna take antibiotics again because I think it causes yellow teeth, I recently made a topic about it. Do you see your teeth turning yellow from it?

I think you should ask your doctor for differin to use with mino, this combination is often used for acne treatment because they work really good togheter, differin makes also the scars fade away faster.