haha, what station you going from?
go to 131500.info and type in your departure station, and put circular quay as your arrival station, then set the time to get to circular quay at 8.30am (30 mins early, plenty of time to get to your ferry, but i always give myself plenty of time, that might be too early for u, lol, plus i dont really know where circular quay train station is, haha).
then you should get 5 or so trips, and it'll tell you how to get there and what time train to get.