I guess I haven’t tried this with Cannabis yet (been doing the water soak), but this is how I start all my vegetable seeds.
I use a 2oz condiment cup w/lid (no holes anywhere), and a saturated 4cup coffee filter folded up in the bottom. The coffee filter prevents the roots from growing into it like they do with a paper towel. Then place somewhere warm of course. The top of my 80 degree grow tent works pretty good.
(These lettuce sprouts got a little overgrown when I forgot about them. Oops.)
How wet did or does the rock wool stay? Are you growing using hydroponics after the seedling stage? If not I would recommend moving away from rock wool and use coco or soil and a solo cup. Rock wool can be difficult even for the veteran grower the 1st few weeks.
48 hour tap water soak and 24 hour damp paper towel.
Dropped in damp soil
Less than 24 hours later they sprouted.
Yes i am growing in hydro. I built an under current recycling dwc. Works pretty damn good too. I just harvested 2 white widow autos that were about 49 inches each! I do use rockwool. Kinda between the clay pebbles. When i get a long enough root to transfer to the rockwool, should i be placing it under light? I do have a seed starter tray with a dome.
I let the seed crack with very little tail when I use rockwool, it can very difficult getting a longer root in the rock wool. I then place them in the seed starter tray under the dome keeping the inside of the dome misted daily for an RH of 65-75%. Once the tap root has grown I then transfer to the net cup and clay pebbles 
