need help going to 12/12

1st grow fill and drian ebb and flow 6x6x8 room 1000 watt hps 440 cfm can fan carbon filter 6x4 tray 50 gal res
im about to switch to 12/12 plants are about 10 inches 3 in rockwool cubes in baskets filled with clay pellets tray is also filled with clay pellets was watering every 4 hours 24 hours of light not sure what i should do now set the timer for once in the middle of the off period 6 pm to 6 am then every 2 hrs in light period any suggestions dont want to fuck this up

After your lights shut off from 18/6, bring the 18 down to 12. It's that easy. peace