What are the details to get member status
https://bitcointalk.org/index.php?topic=237597.0"..The maximum number of activity points you can get is 1 per day, but your activity score only updates every two weeks. Therefore, it will take about 100 days to get 100 activity if you post once per day on average..."
In the next paragraph it says: "Activity is updated every hour."
Probably the rank is what updates every 2 weeks.