a little help here

how big does a seedling have to be before you put them on a 2x2 flood tray system their in rockwool and there about 2.5in tall now?

I know this. I am guessing they are in the 1.5 squares then u put them in something else? Take your 1.5 squares and when the roots start to show through the cubes it is time to put them in their bigger "pot". Wait till they show like in soil when it is time to transplant into their next home. Then you can place them into wither 4 or 6 inch cubes, a hydroton bed, or net pots.
They go on the table of course at any time however no need to flood if they only in little squares, so why waste everything. Also and i am sure you know this the squares will drown, that would be dangerous.
A littl more info would be easier.

i have the hydrton rocks and the mesh pots they are in that little green house you can get at the hydro store yes they are in the little cubes right not and i want to replant in the mesh pots w/ the rocks so you think they are big enough to transplant