The colored range birds take a few weeks longer to reach broiler size than the CX. I will be processing most of my CX Hubbard White Mountains (a little slower and more active than the typical CX) at 8 weeks, I expect to butcher my range birds at 10-12 weeks. Most people I have talked to about dual purpose roos say 4-6 months depending upon the breed. I do know of a few people that have Dels ready to butcher in 12-14 weeks.
I think I am going to continue raising mixtures of CX and Range birds at the same time. It seems to be working really well for me.
Feeding: I throw as much feed as I can (local farmer no perservatives, no antibiotics, etc.) in the evenings giving them enough time to eat before it gets dark. In the am I give them about 1/3 - 1/2 as much and open the pens to let them free range. I want them to have enough food to take the edge off, but not so full that the do not graze. So far it's been working well. My birds are progressing at exactly the rate I was hoping for. I will process 1/2 my CX at 8 weeks, and the remainder at 9-10 weeks. 1/2 the colored rangers will be processed at 11 weeks, and the other half at 12-13 weeks.