I use Rockwool in my system. So Ph the starter cube insert the stem and don't water it, just keep it moist?theres no rule but its easier to handle a 6 week old plant than a 2 week one. older ones dont mind being abused as much.
when theres 6 or so branches with several new meristems on it you'll be golden.
cut the stem at the stalk, scalpel preferred, clean blade, I use a small cutting board. final cut near new growth and scrape a bt to expose the cambium layer, dip in clonex and into a moist cup of pro mix/rooting cube etc. water in lightly mist , dome for a day, uncover and dont water till you see roots coming out. thats what I do for a 99% success.
Here is my rig and future plantsah..I remember rockwool. I liked it, wished it would burn when finished though....
yes soak cube, gently squeeze excess water, insert stem and dome in a warmer/not cooler area.
you can mist once clone once but I wouldnt do it again. I dont know your space but if you keep the cube in a cup
in a tray you should see roots before you need to water. But if the cube feels dry pour a shot of water over it, and not again till its dry.
if its moist on the outside its wet inside. hope that helps