In Wyoming it always seemed to be late september or mid to late Sept. Even in a ground blind you have to be very still as they can see movement from miles away. Make sure you haev the backside closed at all times. I have stalked them if there is rolling hills to hide behind. It is very challenging but it can be done. Our group sat by water holes one day and had some come by but never come all the way in. The other day we stalked and was able to get within range of a few but drawing back is the hard part. One got a shot but mis-judged the yardarge.
Good luck.