Chojubai are pretty easy to grow from cuttings. I usually take cuttings in May, though I think they’d grow most times of the year. I’ve mostly done them without a greenhouse, but they take really quickly inside greenhouses.
As for the length, I try to cut back to where there’s some woody growth. Cutting where the shoot is still soft doesn’t work as well for me. I usually do shoots between 2" - 4"+ though much longer can work inside a greenhouse.
One thing to try would be to wire the cuttings when you strike them. It could be a good way get good movement going as soon as possible.
All that said, the best way to propagate chojubai is by root cutting. Let a plant grow large and then cut lots of sections of woody roots and plant them in bonsai soil.