Select supersaver but from zurich hb as they don't do them to the airport you'll have to get a normal ticket for that part of the journey even though it may be for the same train! When you get to the name and d.o.b section select no reduction then it should show what tickets are available for the times you want,sometimes it says supersaver tickets are unavailable for this journey I had to make 2 bookings because it wouldn't let me book more than 4 tickets at half price for some reason it guides you to full price even though the tickets are available!!!