Google "no mercy" or "12/12 from seed" and you'll find a Dutch method that starts plants off in 12/12 in sog style. They claim that it enables them an extra harvest per year since it's cutting weeks of veg time off each cycle.
Generally speaking, you need to sog with clones of a strain you know the "stretch" amount of. Say you know your strain stretches 2x it's height (not ideal for SOG but just for sake of example). Well then you will know when those plants are 1 foot tall, that after your stretch, they will be about 2 feet tall.
So if the plants are 2 feet and you have to keep your light 1-2 feet above the canopy, that means a good lower portion of the plant will be 3-4 feet from the light.
On the other hand say you flipped your strain 12/12 immediately, it would stretch and grow at the same time, and might only reach 1 foot tall instead of 2 feet so the light intensity at the lower portions will then be much greater.
Some strains really don't stop stretching, like sativas especially, so they may not be ideal for SOG style anyway. Indicas are generally better suited, and especially since they're typically faster flowering, they're the ones you'll be able to get more harvests per year with.