Thanks for your question! Each sitting day the senators and members of House of Representatives meet to conduct business in their respective chambers. These meetings or sittings usually run continuously for 7 to 11 hours.
Sometimes sittings are much shorter. There are lots of reasons this may be the case. For example, on 24 October 2002 the Senate sat for 2 minutes! The reason this sitting was adjourned—suspended—was so Senators could attend a memorial service for the victims of the terrorist attacks in Bali.
You can find a record of the hours the Senate has sat over the last couple of years on the Parliament House website.