Did the automatic reply give you a reference number? And did you fill in all the details on the booking form from their website with your names, which cruise you want etc?
If you filled in all of that detail and received a reference number in the auto reply then likely you will not hear from an agent until they have actually booked you because they have nothing they need to contact you about yet since bookings haven’t opened.
(Also, if you haven’t cruised before then it will be Thursday that you can book the Australian cruises, rather than tomorrow.)