How long it takes depends on how hard you work at it and you have to pay attention to your body. Here's how I work out : Hit it hard for three days, then give it a rest for one day. Then three days again doin something slightly different, but still hitting it hard. If I can be fairly "buff' at my age, then you can surely g-r-done young lady.
Yeah i agree with the above comments. If you work hard for it, it took about 2 to 3 months.
It takes a month to flatten to your stomach if you do a core workout for example plank etc.
depends on how much you weigh I guess. I'd say a month to tone up though. :)