See Fair Work Act 2009 s.394(2)
An unfair dismissal application must be lodged with the Fair Work Commission within 21 days after the dismissal takes effect (please note that if an employee was dismissed on or before 31 December 2012, the application must have been lodged within 14 days). The Commission may allow a further period for lodgment in exceptional circumstances.
Time limits are imposed on making an application for unfair dismissal to the Commission for a reason. A request for an extension to that time is not and should not be treated as a fait accompli.