We will need more info like was the ACDF done with own bone or Donor ect?? Did you have hardware ie: Plate and Screws? Are you in a Hard Collar?
It can take 2 months for the fusion to start and take. Mine took at 1 month and was quite good by three months. At 6 months I will be allowed to ski again. I used my own bone, no hardware and Hard Collar for 2 months.
Some folks claim a full year for fusion maturity. my NS said it won't get much stronger than at 6months (in my case) again I had a rapid fusion due to my own bone and a flawless surgery.
If you have a tough active job, I would think it would be at least 3 months min... a year max if the fusion takes.