From my own personal experience, I would take the CFA before the football season.
Like you, I wanted to wait until after the season with the hope that I would be in great shape and therefore do extremely well on the CFA.
Unfortunately, I twisted my ankle around Thanksgiving right before the playoffs, and I had to walk around in a protective boot outside of practice. After the State Championship, I was forced to rest so it could heal properly. By the time it was 100%, it was the end of January, and I was out of shape and in no position to retake the CFA.
Bottom line, take the CFA before football starts. The risk of injury is high in the sport and you will be in a tough situation if at the end of the season you are injured and you still havent take the CFA...