The short answer: two to six weeks for standard Web sites. The long answer is that it really depends on a lot of factors, including what features you may be looking for—some clients just want a basic, five-page Website, while others want a shopping cart-enabled, inventory-tracking, email-campaigning Website with custom features.
The shortest time it can take to build a Web site would be to relaunch an existing Website -- because it already has most of the content in place, that reduces the time it takes to build the pages with your information on it. In that scenario, it would likely take a week to build the site and launch it with your approval.
We are available for larger projects that could take a year or longer to fully complete -- and we often work in phases in those situations, so that the proper milestones and project objectives are being met.