Visit Duration Goal

Feature Request: I would like a Visit Duration Goal.
Ex: How many visits were longer than 5 minutes?

Reason:
We provide a B2B service. We have few visitors. If a visitor is on our site for more than 5 minutes, there is a 20-50% chance that they will contact us. That is why it is an important KPI. I am currently looking at it on a daily basis, but it would be nice to be able to filter for a period of time.

Thanks in advance!