I was wondering the same thing. I have a buddy that was growing 24/0 and it flowered under low light intensity. June 21 is the equinox so the day length is decreasing after that anyway which induces flowering. I think vegging at 24/0 will work. You could try to increase the day length starting at 12/12 untill you put them outside which should give you the longest veg. growth and largest size if you have good light intensity and are not worried that they will have time to mature fully. I guess that it would depend on whether that particular strain would have the time to finish properly at your lattitude under outdoor only conditions