It's all rather dependent on if/when an editor decides to do some work in the category for that particular niche. Since our editors are all volunteers who donate their time freely, we essentially allow them to choose when and where they would like to work. (We get a lot of suggestions, so there's always plenty of places with work to be done, not to mention the fact that reviewing public suggestions isn't the only thing that editors can do to help build and maintain the directory.) It's therefore not possible to predict when someone will next be working in a particular place, nor how long a given site is likely to have a wait to be reviewed.
A case in point is my editing tonight. I am allowed to edit in any part of the directory I choose, and since I have a warm spot in my heart for the Regional/ branch of the directory tree, I usually stay fairly close -- and if I wander away, I usually wander back reasonably fast.
Earlier today, I spent some tim working on military aviation caregories, tonight I cleaned out a few dead links in Arizona, jumped over to Delaware (darn, no frequent flyer miles!) and added a few sites that a colleague recently "mined" as part of an informal project to beef up that state. Then I decided to visit a place that has been a vacation destination of mine for many years, Baguio City in the Philippines. I was dismayed to find only one site listed, and a handful awaiting review. I cleaned out the sites that were waiting, mined a handful of others, moved up a level to the Province, rooted out a few dead links that hadn't been found yet, and moved a site into Baguio where it was better suited. Now I'm in here, and while it is bedtime, I may just jump back into Delaware and see what I can do there. Last night, just for kicks, I edited in The Federated States of Micronesia for the very first time. Why? Because it was there and I had never edited there before.
Just a typical night of editing while the spousal unit is asleep.