In the past it was up to the moderator of the board you posted on the most. There was no specific number of posts or time period, but they looked at your posting history and if you had a decent posting history and didn't break the posting rules, they would unmoderate you. Now that there are no moderators, it goes through the TER staff. Maybe now they do have specific criteria only known to them, or it may be that they still just play it by ear, and check your posting history, and make a subjective decision. I would suggest you contact admin and ask them to unmoderate you, then you will either get unmoderated, or you will get an answer telling you what you need to do.

On another board I belong to, they are very specific. You have to be a member for 6 months and have at least 25 posts, so even if you have 200 posts in your first 3 months, or if you are member for two years but only have 24 posts, you will still be moderated there. It's kind of weird but at least the rules are in black and white so everyone knows them.