My feeling (and this is strictly personal, not official at all) is that you should be willing to plan to spend 1/2 hour or so every week. That will give time to do 3 or 4 good site reviews, or a good Google search on some related subtopic, or check out the "red zone" dead links within a week. Less time than that, and I think you're likely to get out of the editing habit.
Caveat: your mileage may vary: some people may be able to regularly spend an hour one Sunday a month, or some such. And, of course, the meta that processes your application may not pay sufficient attention to my opinion.