Hello, good question. Once you sign up and get approved then you can add the code to all your sites regardless of the traffic. I put up adsense immediately on all the sites that I built or bought. Made no difference. You just don't see any cash rolling in until you hit like five bucks a month. that is a lot of traffic so it takes about six months to see some traffic, if you do it organically, that will start to bring in a couple dollars. I was just an average marketer that was doing the seo myself. It took about a year to make 15 to 20 dollars a month on a good site with good keywords. That is why you have to have hundreds of sites to make a living. Many people automate and use outside labor to update their material and put in relevant video. It is a tough game but if you are just sitting home anyway you might as well.