Zygomatic arch broken 18 days ago, is it too late for a surgery? (Photo)

Dear kk47In general, if you are having difficulty opening your mouth, then reduction of the fracture at any point is an important consideration. If not, then its essentially aesthetic in nature and not necessary. 

Thanks for the question, the bone may be too strong at this point to just pop it out. Unfortunately its a tough area to get too surgically without big scars. I would suggest seeing a craniofacial specialist in your area, sometimes I have just put some filler in the dent to avoid surgery

Thank you for your pictures. Your fracture is 18 days old and maybe healing already. It may be too sticky to reduce at this point. As long as you're not having limited or painful opening or a cosmetic deformity a from this fracture treatment is not necessary.

Isolated zygomatic arch fractures can be reduced through a
Keen (through the mouth) or Gilles (through the scalp) approach. As the bone
heals, the bone becomes more difficult to reduce (put back in place);
therefore, the bone should be reduced as soon as practical. The long-term
success of the reduction is dependent on multiple factors. Often the reduction
is unstable (does not stay reduced) because of the action of the muscles on the
bone and / or because of the multiple bone fragments. In these situations,
patients may have to either accept a slight bony deformity (depression) or
consent to reduction and internal fixation through a more invasive (coronal)
approach. A detailed examination and review of a CT scan of the face
will help delineate the best surgical option. Consultation with a plastic
surgeon would be the next best step.

it is not necessary to fix all facial fractures. Surgical intervention is determined by several factors. If you have no facial deformity and/or painful mouth movements like chewing or malalignment of your teeth, then there's no indication to fix the fracture.

At 18 days the bones are trying to heal, but with some effort and skill, the surgeon should be able to improve the position of the in-fractured zygomatic arch.  But get this done asap, as it's trickier to correct the deformity later.  Best of luck.