Google announced they changed the workflow to sign up for Google AdSense to make it faster. Now, after you sign up, you have immediate access to your AdSense account. In the past, you had to wait for an approval email from Google to gain access to your account.
This means that you can begin creating ad units and place them on your site even before you are approved, so that when you are approved, the ads go right up on your site.
Google said that it takes typically around "48 hours for our specialists to complete the site review after you add the code to your site."
Here is the new sign up screen:
Forum discussion at Google+.