There is also another subparagraph in 214.2 where the eighteen hours is mentioned.
But the point here is that, taken in isolation, this paragraph does not say much. One should read all 214.2 paragraph or at least what comes before the 214.2(m)(9)(iii), since this bit is a condition for something which is stated before. Try to post the whole 214.2 and see if the picture is clearer ;-)