It took 5 days to get my first $100 this month. The original $100 took 6 months of ads plonked on a site and not looked by myself followed by 2 months of actually learning how to use adsense and tinkering.
It took me around 12 months, I set up the account on a minor blog I had and made around 75c in 9 months. I then set up my main site and it took me around 3 months to convert to $100. I now get paid EVERY month and this month has been a record. I am $2 short of $500. My Adsense earnings have increased with my SE traffic, the more SE traffic I generate, the better my Adsense earnings. Also, I have finally woken up to the fact that you need to work at your ad placement etc and its paying off. I still have a long way to go with my other sites and then you never know where it could end.
It took me 7 hours. But... My site was already receiving traffic and 7 months old when I signed up for adsense A new site, usually takes me 1-6 months, to be making 5 dollars a day. I don't make adsense sites anymore though, or put adsense on new sites. There are much better ways to monetize your traffic. Selling a product, is my fav way. Gets me more active, because I have to pack boxes and ship them, and much more profit from selling the goods than selling a click to someone who sells the gods.