Customs in Auckland and Sydney?

Hello. I'm flying to Australia in July of this year, from the U.S.
I land in Auckland, layover for 2 hours, change planes, fly to Sydney,
and have another layover (hopefully only 2 hours) before flying to my
final destination.

I'm wondering about going through customs in Auckland and Sydney.
Will I have to go through twice? How long should I expect it to take?
The reason I ask is that I have a choice of bookings for the final
leg of my flight out of Sydney. I'm afraid that 2 hours won't be
enough to make it through customs, but my next choice of flights out
of Sydney means an 8 hour layover.

Does anyone know? I appreciate any info!!

TIA,
Stella
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