I've been building websites for over 25 years, and the funny thing about building with AI is that the job did not get any faster at all. What has changed is the nature of what we build. It's a real Jevon's paradox.
In a day: Don't believe the hype, there's no "single prompt" website. Sure, you can do it in a single shot and it will not be terrible, but in the same way as a default Wordpress installation would not be terrible – but not the thing you want to ship.
A week: sure, you can make a real nice one, as you always could, but it depends on your definition of "nice". Back then, if it worked on Internet Explorer, it was considered nice enough. Then Nice became a little flash animation. Today what is considered a "nice" one is what would be a month's worth of work before – but since the expectation is higher, it just becomes the bare minimum.
A good product will take weeks or months. The difference is what you build in that time. In two weeks I will have built, rebuilt, redesigned, thrown away and recreated 4 versions of the same site. What would require a long meeting between manager and designer and developer, then to build a single feature, becomes something you build as a test. Alone. Things that you'd only build later, like tests, scripts, deployments, improvements, you get for free on the first session.