I played with rooting the flower cluster wood this past spring. One of the Annie Laurie McDowell cuttings callused perfectly, but sat there, doing nothing. I've kept it watered and in partial shade in the 16 oz. foam cup in which it was originally planted. I didn't give up on it and it hasn't given up on me! This is what it looked like this evening.
It's taken nine months for the callus to generate this brand new basal. So, when your cuttings remain green, but appear to not being doing anything, take heart. There IS hope!