See Fair Work Act s.383
The minimum period of employment is:
The period of employment starts on the date the employment commences. The period finishes on either the date the employee is notified of the dismissal or immediately before the dismissal, whichever is earlier.
A month means a calendar month. A calendar month begins on a date and finishes immediately before the corresponding date in the next month.  For example, a period of 6 months commencing on 26 February 2009 would finish at midnight of 25 August 2009.  If there is no corresponding date then it finishes at the end of the next month.
An employee’s period of employment commences on the employee’s first day at work.
 Wilkinson v Skippers Aviation Pty Ltd, PR903635 (AIRCFB, McIntyre VP, Cartwright SDP, Harrison C, 30 April 2001) at para. 31; citing the Acts Interpretation Act 1901 (Cth); applied in Prigge v Manheim Fowles Pty Ltd  FWA 28 (Richards SDP, 7 January 2010) at para. 10.
 Corner v SkyCity Adelaide Pty Ltd  FWAFB 955 (Cartwright SDP, Ives DP, Rafaelli C, 15 February 2011) at para.7, [(2011) 204 IR 63].