sorry m8 missed the update.
you flood it untill it hits the over flow pipe then shut off if you only have a 15m segmental time just leave it go 15m then let it go off it does not matter you will not drown the plant. you will need a cover with holes cut out for the pots or the new root growth will die off. you could fill the table with clay and do away with the top cover, but still put the plants in pots or when you flood the plants will fall over.
you are only using a small table my self i would use both > fill table with clay and put a cover over to stop evaporation less salt build up more stable ph and the roots will fill the table by doing it that way you will not have to flood so often and the feeder tank will need next to no matinance.
WHAT EVER YOU DO WASH THE CLAY AND PH IT BEFORE YOU START!!!
punch holes in the clay bag run water through it to get most of the dust off find a big bucket make up ph water to 4-5 put clay in and let sit 24 hours take a ph reading see what it reads ? you want it anywhere from 5-6 ph if it is then start filling your pots and table with the clay.
that will slow down if not stop the ph rising 99 times out of 100 the ph will rise in any hydro system so if the rocks are around ph5 then after a day or so it will rise to around 6 all you need to do is keep the feeder ph around the 6 mark and you will have no problems.
12/12
only another 8 or so weeks left to go! get some pics up lets see how they are doing.