I have only planted favas in zone 9 so I can't directly help with timing, but I want to make sure that you and responders are aware of the possible approach of using fava beans as a cover crop. The point is to fertilize the soil. I assume you would plant them soon in free garden areas and let them grow until they freeze. Assuming they went to seed, the object would be to collect them for next year's plants and not to eat them which can be a problem for some people anyway.

Hi spinon
I am in upstate NY, I have planted fava beans in early spring and harvest them by the end of June or early July. Some people plant them in october and again in June so to have the beans twice in one year. I have never planted them in October, but I am gooing to try this year. We like the fava beans alot and if I can have them twice in one year I'll be very happy. It is important the the soil is slightly sloped and well drained otherwise the seeds will rut.

Our local demonstration garden one year tried to plant it in the fall for a very early spring harvest. We are in zone 7 and the beans sprouted just fine but didn't make it through the winter. I am tempted to say that zone 6 might be pushing it but if you don't have anything to lose you should try a few anyways. :)