First time - will 3 days be beneficial at all????

I'm very keen to try the Master Cleanse. I've heard that it is best to build up to fasting gradually - a bit like running (you wouldn't attempt a marathon first time.....) So, I'd like to do it for maybe three days. I'd still follow all the instuctions and do the salt cleanse. Would this do any good or does it absolutely HAVE to be for a minimum of 10 days for there to be any real benefit?

Thanks to anyone who can give advice.

Maxine.