Certification processing times are dependent on multiple factors such as credential recognition processing times as well as registration times. Credential recognition typically takes  6-12 weeks from the time all required documentation is received. 

Registering with the OCSWSSW (Ontario College of Social Worker and Social Service workers) is not mandatory but you will not be able to practice or call yourself a social worker or social service worker in Ontario. You will also be ineligible for any jobs that require a social worker or social service worker. This results in less opportunities and a lower pay level in most cases. 

General requirements is the completion of a 4-year full-time university degree with the completion of required social work courses as well as a minimum of 700 hours of field work. Recognition is done on a case by case basis though. 

You will have the opportunity to appeal the decision directly to the president of the Canadian Association of Social Workers. (subject to rejection if there is not sufficient information/explanation to justify an appeal. 

You can start the process right away! The sooner you can start, the better. Credential recognition can be done before arriving in Canada and is sometimes easier to be done from your home country as communication with your educational institution is required.