Take bigger cuttings with thicker stems. Gives them a jump on rooting and they only need to soak for 20 min I have tested every time period and it does not make a difference.That AND I feel like the rockwool really needs to be precharged for a day in a rooting solution. then I hate that you can't really use the damn hole. why do they make that fuckin hole so damn big!
Also press the edges of the hole around the stem to make a snug fitting.