About a week. Back in January 2004 I bought a domain, a design template and set up a copy of the free osCommerce shopping cart. I created packages of advertising services, put them in the store, then started posting on webmaster forums with advertising sections, and participating in the forums with the site in my signature. Total time from idea to working website was two days.

I got 5 orders the first day, a couple the next, a few more the next day, then I started advertising on search engines. Sales exploded. Over $100,000 by the end of the year... which is a lot of $10 sales!

I was simply buying up different types of ad space at wholesale rates from various networks/services, then packaging it in smaller chunks for individual site owners in the $10-40 range. The site paid for itself in its first week. A few years later and net profit, rather than revenue, was past six figures as well.

I'm not so much in that business anymore, but it was my first entrepreneurial endeavor beyond slapping ads on articles I'd written, so I was proud of that success. I later replicated the story several times with products that were income-you-could-live-on-full-time from the day the websites went live.

I really need to do it again, too. I've since sold off those businesses to pay for two college degrees, then for a new car and downpayment on a home... while my current freemium+premium services bring in enough to cover the mortgage, I need to get back into product building to get some money in the bank again.