tor: how to change exit nodes automatically (every 30 minutes)

I am ruing tor (OSX browser), and then using it as SOCKS5 proxy in another app

It works great in the other app, but what I would really like is for a new exit node to be updated automatically every 30 minutes or so. At the moment, as I understand it, if I just leave the tor browser ruing (empty), it will keep using the original exit node, and therefore never change IP address.

Any ideas?