I think a ring group with no valid extensions will instantly hit the exit action @Kenny Riley, despite the delay.
My lazy solution was to upload a WAV of a ringtone and play that in an IVR before hitting the next destination.
The real question I have is why do you want to do this? I just can't savvy why you want to delay your calls getting to their endpoint. I'm for getting to that answered stage in the shortage possible time. Introducing an unnecessary delay however short just doesn't seem to make sense.