I've had them grow when planted late - I've mixed them with other things.
The deer really like the yound soybean plants in August/Sept - and they can pick off the young plants in a hurry!

You really need lots of Nitrogen, and good moisture (shouldn't be a problem this year!)
to get much size in 6 weeks before a killing frost.

Personally - I'd go back over it with Turnips/Rape seed - so that when a frost does come in Late Sept - the field isn't all done for the hunting season.

FH