first you shouldnt have gravel you should use lava rock or clay pebbles next you just waterfrom the top until the roots grow into the water and i keep my level about an inch from the bottom of the baskets
im not sayin they wont root but i think that because the plant was in flowering putting the clone back into the veg stage could cut yields and possibly hermie it let me know if im wrong tho it would be nice for me to be able to cut some clones now
i would just start it at about 20 get a thermometer and watch theplants if they start stretchin move the light down there can be a lot of variations but i dont think you want it any closer than 12 inches