Its just like grow your account and get more benefits from the forum. You need to increase your rank to post with less time gap.
You are wrong. The allowable timegap between posts relates to users' activity points, not ranks. In the past (before the appearance of merit system), activity points totally relate to ranks, but it is not the single factor now. A shit poster can get 1000 activity points but might still be a newbie if won't be able to get a single merit.