How long will it take to treat diastema with braces?

Depends on cause: Is it size or angular ion of teeth, interference from opposing teeth, heavy tag of tissue between teeth, or many other reasons or combination of above. Orthodontics is a service, not a product. Everyone is different. See a qualified orthodontic specialist for evaluation of your unique problem and your best unique solution.

See Orthodontist: Most diastemas require a full set of dental braces and retainers. You need to consult orthodontist and get diagnosis treatment plan accordingly.