I'd put the light up to about a meter until the plant starts rapid vegetative growth, I can't really tell you when to switch to 12/12 as I don't know the size of your growing area or what style you want to grow the plant but I'm assuming as you are using a 600w that you have at least a meter square and if that is the case I would veg her out big. do lots of training to bush her out and be patient at least wait until you see pre flowers.
Yeah when they start vegetative growth go back to around 70cm, I would highly recommend starting a grow journal you will receive lots of friendly help.
Spimp Yes you are right when you write comment i go to check site where i buy seed and i found AK48 is a Cannabis Indica/Sativa hybrid, How tall plant could grow ?