XF 2.2 User group promotion after X days of joining another user group

[Orit]

Hello,
We have a private forum where only a specific user group (we will call it user group A) has access to it.
Users can ask to gain access, and are accepted to that user group or rejected.
In order to give members time to get used to the forum we'd like to give new members of that specific forum less privileges for about 2 weeks.

I thought of creating another usergroup (user group B), and set up a promotion to user group A 2 weeks after they joined user group B
(Just as I would have done with new members to the board).

Is there a way to do that?
Any add-on?

Thanks!!