Thank you for your replies!

I checked Jetstar but there seems to be no flight in the afternoon. Only 7AM and 9AM.
Also the other websites don't offer much more.

I am not sure the 14:15 flight is more expensive because it's packed, but probably because it's direct. I think I will end up buying that, since after a 30h trip from Europe the idea of having yet another connection doesn't sound so grand.

Silly question: even assuming that the SQ agent in AMS would be able to do it technically, could I check my luggage through all the way to ZQN? I think I will have to get it in AKL anyway to clear customs, right?