I have had the same problem and have set the time to disconnect after 18 seconds, this supposed feature is in Outbound calls and settings at the bottom of the page if i remember correctly, but it does not work for me either if anyone knows why it is not disconnecting i would love to know as well. I also find the system very unstable and freezes after dialing a few numbers. iF IVM would just disconnect it would be bearable!
Please let me know if you have any success.