About an hour for me a few days ago. I applied on the iPhone site, paid for it on the Apple store site, then about an hour later got an email with a link in it and a code.
There was a glitch. I clicked the activation link and it opened the iPhone site page, which I already had open, and nothing was different. After a while I thought to log off the site and click the link in the email again. When I did it this time it took me to the iPhone site and to a page where I could activate my account. After that there was a portal link on the iPhone page when I connected to it with all the additional stuff on pages inside the developer portal.