I have some NZW does that came from the TAMUK Rabbit Research program. They just turned 16wks, or 4 months. I checked them both for "readiness"...one still white, not ready. The second one, hot pink/purple, indicating readiness. She also has been displaying other behaviors that tell me that she is ready, ie. humping her cage mate, flagging her tail, etc. I put her in with the buck and she lifted twice. Now, I know that a lot of folks will disagree with me, but I am using the commercial standards for breeding. If they appear ready, I will give them a try. If they run, clamp their butt to the wire, etc. I will remove them and wait a while. I let the rabbit tell ME when SHE is ready....JMO...YMMV.