These temperatures should be maintained as constantly as possible during the germination period. If you just squeeze a corner of a cube, water should come to the surface. If it does not then you should give the whole tray a sprinkle of lukewarm water. The biggest mistake with Rock Wool is to keep it too wet and this usually occurs through poor drainage. Once your seedlings begin to appear you will need to give them plenty of light, a warm sunny windowsill might do but a greenhouse or artificial light will be best.
Fluorescence are very suitable for small seedlings or clones.
It is still important to maintain temperatures in the mid twenties for as much of the day as possible. Keep checking your Rock Wool cubes for signs of drying out. Once your seedlings begin to show roots at the bottom of the Rock Wool cubes it is time to think about planting them out. Just lift the little cubes carefully out of the tray. Your new seedlings are now ready to plant into soil in the normal way OR to be cultivated further in Rock Wool or other hydroponics systems.