Acts Interpretation Act 1901
In any Act, a sitting day , in relation to a House of the Parliament, is a day on which the House actually sits. 2M(2)
However, if the House sat without adjourning on a previous day (the earlier sitting day ), any period during which the House continues to sit, with or without a suspension, on a later day, until it adjourns, is taken to be part of the earlier sitting day.
The Senate begins sitting at 9 am on Thursday and extends (with or without a suspension of the sitting) until it is adjourned at 3 pm on Friday. Thursday is a sitting day for the Senate but Friday is not. This example applies equally to the House of Representatives.
The House of Representatives begins sitting at 9 am on Wednesday and extends (with or without a suspension of the sitting) until it is adjourned at 1 am on Thursday. The House of Representatives then starts sitting again at 10 am on Thursday and adjourns at 3 pm on Thursday. Both Wednesday and Thursday are sitting days for the House of Representatives. This example applies equally to the Senate.
For the purposes of this section, a House is taken to have adjourned if:
(a) the Parliament is prorogued; or
(b) that House is dissolved; or
(c) if that House is the House of Representatives - that House expires.