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.
The 21 days for lodgment does not include the date that the dismissal took effect. This means that day one commences the day following the dismissal.
If the final day of the 21 day period falls on a weekend or on a public holiday (where the Commission is closed) the timeframe will be extended until the next business day. Public holidays or weekends that fall during the 21 days will not extend the period of lodgment.
The Commission is closed on the following public holidays (or substitute public holidays):
On state or local public holidays (such as Queen's Birthday) the local Commission offices will be closed however electronic applications can be submitted. A hardcopy application can still be made at the local Commission office on the day after a weekend or public holiday (if the final day of the 21 day period falls on that weekend or public holiday).
 Fair Work Act s.394(2).
 Acts Interpretation Act 1901 (Cth) s.36(1). This Act as in force on 25 June 2009 applies to the Fair Work Act (see Fair Work Act s.40A).
 Acts Interpretation Act 1901 (Cth) s.36(2). This Act as in force on 25 June 2009 applies to the Fair Work Act (see Fair Work Act s.40A). See also Hemi v BMD Constructions Pty Ltd  FWC 3593 (Richards SDP, 12 June 2013); Cahill v Bstore Pty Ltd T/A Bstore for Birkenstock  FWCFB 103 (O'Callaghan SDP, Gooley DP, Williams C, 9 January 2015); Stedman v Transdev NSW Pty Ltd T/A Transdev Buses  FWCFB 1877 (Harrison SDP, Lawrence DP, Cambridge C, 20 March 2015); Boyd v MarketTrack Global Pty Ltd T/A Numerator  FWC 8489 (Dean DP, 16 December 2019).