Apparently its (fresh garlic juice) to be kept just for twenty minutes or so and once a day is enough. Mind you, the skin burns and may turn red for a while- so just be prepared to expect that reaction (the more the mess in the skin the more it will burn.) Be careful when you wash it off- don't scrub it hard- just rinse it off lighly.
I have not used it for long enough myself- so don't have first hand experience- but have heard a lot of good reviews.
Incidenatlly, I found something that works really well. I have been using liquid Bentonite for the last few days. I use it as a substitute for soap and I use it as a face mask too and that has really helped my skin tremendoulsy. My face is almost as clear as new exept for a couple of Acne pimples.