It waits until someone volunteers to do it. And yes, that can be more than six months.
"Supervision" in this context involves making sure that people do a good job of what they volunteer to do. The military concept of volunteerism never really caught on here.
Note also that you're misunderstanding the purpose of the "suggest a URL" feature. It's not to force anyone to review it. It's to help reviewers find good sites, that's all. That you suggested a site doesn't even give it a priority over sites that weren't submitted at all!
Here's how one volunteer editor works. I currently have two other browser windows open. One is devoted to pushing legitimate site submittals past the spam filter. The other started out reviewing sites -- not, however, finding any that were appropriate for the topic. I ended up doing my own web searches for good content. I don't care how long those sites have been up, or when or even whether anyone ever submitted them anywhere. I'm finding good content, and I'm listing it.
Yesterday I also got involved in some categories mentioned in resource-zone. I deleted some egregious spam, redirected some obvious mislocated submittals, and tried to clean up a bit, so that next time an editor with local knowledge and interest visited, they wouldn't be put off by the mess.
And I'll stop editing today, just as I did yesterday, confident that I did a good job, even though there were several hundred thousand other submitted sites (and who knows how many unsubmitted sites!) I could have looked at, but didn't.
That's the way we work. Yes, we know some sites wait more than six months after being created, let alone being submitted. No, we don't know which ones they are, and if we did, we know it would not be good for the directory to make them a universal priority. (And, sigh, if we did, six months wouldn't get you near the top of _that_ queue, either!)
We get more work, and better work, from people working in their areas of interest and knowledge.