I always question how long an article should be, but then I reliase... Even if 30 mins is too much, if it saves you much more time googling around, it is worth it.
I want my articles to be used as future references, to be comprehensive and self-contained. I want them to be useful both to the complete beginner and to the person who already know most of the stuff.
After gathering some feedback I am now considering extending it to include the difference between structural recursion and generative recursion and differences between memoization and Dynamic Programming.