How long to see roots??

I have 2 girls in some net pots with lava rock about 3/8 of the way up and than a 3" rockwool cube and more lava rock. How long until I see the roots through the bottom of the net pots????

Come'on someone has to have at least a guess...all this grow knowledge and no responses.

hey, i started my first hydro grow this week, i am on day 7 now i believe, and my roots started to show at the bottom around probably around day 5-6. Doesnt take that long, roots grow fast.