I have a small army of alts for which each ran the turbulent dungeon quest (five turbulent dungeons) at the end of which you receive a heroic piece of gear. Having done so also seems to count toward the Timeways III achievement which rewards the mount.
Doesn’t seem to matter if you run one character over five weeks or more characters for less time (mine were all level 80). What appears to matter for the achievement is having the timeways buff while also completing the twenty five turbulent timeways dungeons and doing so with multiple characters reduces the time necessary.