Your thoughts aren't wrong by the way, time can mean activity, and that's baesd on how often you post, if you do not post at all, you'll not rank up. Quality posts gets merits, so this also covers that part, merits are given to quality posts and those merits are what enables you to rank up. So on your thoughts, If you spend your time on the forum making quality posts then you'll rank up.  
Just one month ago and your post history "reads" bounty reports only.