you want to get a good root system going.. period, they are the heart and soil of your plant. now like the other posts suggest you can transplant right after you see roots about an inch long come out of what ever "starter" your using, rockwool etc. (i use rapid rooter's). but i would personally get those roots as long as you can, someone told me to try to get them as long as the cutting you took (around 5 inches). this is so the plant grows alot faster and gets all uptake of food you give it. if your just using a tray and humidity dome with some florescent lights then you should be fine, very simple:
-if your using rockwool you have to soak the cubes for 24 hours in 5.5 ph balanced water, u can also add some low veg. nutrients to this. (the glue in them has a more alkaline base so you need to bring this down a bit, check the ph of them after soaking if you want, it should be around 6-6.5 or so)
-keep the lights on 24 hours
-spray clones and dome with ph balanced water once a day
-open vents, or keep dome slightly open for one hour a day (best to spray after this)
-use some low veg. nutrients and fill tray (about 500ml or less depending on size of tray, mine holds 50 rapid rooter's) (replace every 3 days ruffly) (might not have to do this if you stay on top of things and make sure it stays really moist in the dome)
once they are rooted well as i mentioned above you can transplant them into some small pots, but not too small because you want these roots to become well established, feed them low nutes after u transplant them, wait till they dry out about 3 days later (i use pro-mix HP for my entire garden which is a soiless mix, has no nutrients in it) then water them, then wait till it drys out again, then you can increase the nutes a little bit, then dry 3 days, then water, and so on, create a schedule.
