First of all, this thread should be in Meta Section. Your answers will be found there.
Second, it updates every 14 days and will increase up to max of 14 points, for those 14 days.
that's kinda wrong, actually
activity is updated approx 1 hour after you're active and every hour after that.
it will keep increasing until you reach your activity limit, which increase by 14 for every two weeks period you posted in.