Deadline to change flexible ticket
 

I need to change the dates on an upcoming flight, but the dates I want will not be in the bookable range until a few days before my flight is scheduled (W fare/healthcare heroes ticket). What is the typical deadline for changing an existing booking (before initial flight)?

4 hours before the flight but I would do it no later than 24 hours

According to an agent I have spoken to and also a remark in the top of manage my booking, for Australia it is 3 days at the moment due to the limited available seats.