Log-on time has nothing to do with activity. And you have to be actively browsing for the time to go up. For activity, simply put you get 14 points every two week period. You need to make at least one post in every period to collect those points. Next period starts on Tuesday and you can get another 14 points then.
I see, that's why my activity is 28 :-)
Thank you for your answer!
hilariousandco already explained you the way activity works in a clear and easy way; however, I may suggest you to give also a look to this helpful thread: ===>>> https://bitcointalksearch.org/topic/forum-rankspositionsbadges-what-do-those-shiny-coins-under-my-name-mean-178608
Nice summary of the ranks but your answer explained to me everything I needed to know.
Thank you again for your time and help :-)
