I try to run my hand over every rabbit's back daily when I feed them their morning hay and supplemental grains, etc. You should be able to feel the bumps of their backbone, but it should feel rounded, not spiky and protruding. Their needs vary depending on the weather- in winter they use more calories trying to keep warm, whereas in warm weather their needs decrease. Their needs also change according to life stage and use- growing, production rate, etc. A hands-on inspection will do you more good than arbitrary rationing, and you can adjust feed accordingly.
I free feed hay and supplement in rotation with oats, barley, BOSS, and CalfManna. Pellets are available at all times for producing does and "grow out pens", and they get oats daily when kits leave the nest. They all get small amounts of vegis and weeds which will hopefully make up more of their diet this spring. I feed pellets at night, and adjust the amount up or down depending on if there are any left in the morning. I want to see an empty feeder. Most get 3/4 cup of pellets daily, but I have some (bucks primarily) who will only finish 1/2 cup, and others (mostly does) that will eat a full cup.
I raise Standard Rex, which are smaller than NZ's I believe. I am new to keeping rabbits as production animals, so my regimen is still evolving. I've learned a lot here on RT. It is a fabulous forum with lots of very helpful members, and the more time you spend here the more you'll learn.