SEQ base you won't get many, SYD you might get the odd international trip or be sent to other ports for a few days but it's super easy to swap out of if you don't want to go.
Jetstar itself is a very 'no overnights' airline but they love the casuals because they are so flexible, can change your duties and roster instantly and they don't have to pay you overnight allowance.
Obviously, overnights aren't guaranteed so go in expecting none but Syd base def get a few but one a month is probably an over estimation- some crew get them regularly others haven't had any in years