The Aristotelian Question of Time

If time is a quantity, why should time when form a separate category? If the Aristotelian say that not only it has been, and it will be, are time concepts, but yesterday, and formerly, which are varieties of there has been, are also time concepts. For instance, they say both that when is in time, without being time, and say that when is that which is in time. Therefore, if some new category is to be introduced whenever one thing acts in another, we might have to introduce many additional categories. The Aristotelians grant that here indicates the same place as Athens; consequently, this expression is equivalent to being in Athens.