a) About a month or so.

b) My hair was limp and stringy and my scalp became greasy in less than 12 hours.

It's very important to find a good conditioner that suits you. I experimented a lot in the first two months (cones vs. no cones, diluted vs. undiluted, with or without ACV rinse etc.). Now I CO every third to fifth day and clarify once a month and my hair and scalp are both very happy