Work Visa - Duly Authorized Certificate and Letter, How Long? Process Time?

I received confirmation about 3 weeks ago after sending my Medical Form that the school I shall be working at started the process of applying for the Duly Authorized Certificate and the Letter of Authorisation. Does anyone have any idea how long this process takes? I will then need to apply online and attend an appointment and I am worried that my time is running out?

Please help,

Leanne