How does variable points work?
Lets say you don't want new members to have any impact on the content, you can set them at 0 and they won't count towards the group moderation. You have another group that is for your average members, you can set their points as 1 (or anything else). Lets say there's one more group for your well known members, you really trust them, so you want them to have 3 points (again, this can be any number). Your point threshold is set at 10.
It doesn't matter how many poeple in the new members group report the content, it's not going to do anything.
It would take 10 of your average members to hit the threshold.
It would take 4 of your well known members to hit the threshold (3 would only be 9 points).
The points don't all have to come from the same group though, so you could have 2 well known members report the post (6 points), 5 new members (0 points), and 4 regular members (4 points) report it and the threshold would be hit.
When do the points expire?
They don't, the points get reset whenever a post (or profile post) leaves the moderation queue.