you should get them to 12 hours lights on - 12 hours dark right away. Then just let them grow until you have to cut them, they wont be ready before the end of september... they might not be all the way ready then, but what else are you going to do. So yeah, 12 on/ 12 off. And make sure they aren't being lit when it's suppsed to be dark, you know what I mean... no light leaks.