The reason for the maximum length was that many people were just creating year-long trackers for no reason (tests, etc), thus clogging up the tracker list. Trackers are meant to be used for defined clan competitions, not just general progress tracking or clan stats (which is what RuneHead is for). What you describe is really more of a progress tracker, not an official clan competition.
However, when I make the next round of updates to the trackers, I may consider increasing the max time frame to 6 months or a year, as the clan competition page is pretty filled up anyway as it is. Also remember you're always free to just create 4 trackers for the four seasons of the year.