Are you saying August 1st the stallion was with this mare?
At this point it does not really matter. You will know when the foal comes out if it is mature or not. Just watch the mare. I would certainly have her in a stall at night if she is bagged up and a halter alarm on her.
It is so much easier if ultrasounds are done on the mares during breeding season if possible so that you KNOW your mare is in foal and how far along.