The Maximum is just what it says the max that that case can be, anything under it to a point is fine. What most people do when trimming cases is to measure all the cases to be trimmed and then trim them to the shortest on if it is below max, if all are above max then at or just under max would be best.
Something to remember however is that unless your cases are above max length you really don't need to trim them, most who do trim are looking for that little bit extra in accuracy of every single shot, ie being able to hit a nail on the head instead of scraping the side of the nail kind of thing. If you are loading for just hunting and your cases are all close in length with none being over max you will be fine. If you are looking at sub MOA then need to trim.