Basically, he's saying when he gets two tasks of the same type, will they add-on to the current expiration date, or just replace the current one.
Yes. Whenever you get another task, while you already have that same task running, it will only add onto the task. Not replace it. Therefore, if you had two Small Toon tasks, and you returned them both at the same time, you owuld get 60 days instead of only 30.