This is surprisingly complicated. A good percentage of the training and the accreditation were related to the calculation of this month.
The Attorney General's Department sent out a fact-sheet earlier this year, clarifying "one month" and giving a bunch of examples. A few months later they updated the fact sheet: I think even they had messed it up first time round.
I'm pretty sure there's an Act which specifically defines this, and I think it goes back many decades. Alas, I can't be bothered finding it now because I have to go to the pub. ;-)
Edit: here we go. The marvellously named "Acts Interpretation Act" of 1901 (https://www.legislation.gov.au/Details/C2016C00691).
2G Months
(1) In any Act, month means a period:
(a) starting at the start of any day of one of the calendar months; and
(b) ending:
(i) immediately before the start of the corresponding day of the next calendar month; or
(ii) if there is no such day—at the end of the next calendar month.
Example 1: A month starting on 15 December in a year ends immediately before 15 January in the next year.
Example 2: A month starting on 31 August in a year ends at the end of September in that year (because September is the calendar month coming after August and does not have 31 days).