I built a bubble cloner and I also bought a daisy 8 cloner...same success with both, about 95%.
Sometimes I get roots in 3-4 days and I have had cuts go over a month with no roots.
There are so many variables in a cut throwing roots that you just have to let it do its thing....unless you are running a production line and can't wait. As long as it stays green and vigorous it will eventually throw some roots.