if your indoor than you decide what time of day it is for your lady.. as long as you go 12/12 cycle she'll start to flower. I've heard of people go slowly down last week of veg. IMO its kind of a waste of time i found, try it straight to 12/12 next time see what happens. the reasoning is once the plant reaches a full 12/12 is when it starts to get into flower mode, at that point she'll begin to slowly absorb more nutes and water for and stretch in growth for about 2 weeks (its like veg growth but twice as fast), then she'll begin the actual flower growth where the little hairs and buds start to go come up. soo that week of you slowly cutting down the light time could be the first week you go straight to 12/12 and she's gonna grow much faster during that first week period of 12/12 than she will in "a little less light veg growth".. I can see your argument of less stress to your girl by small amounts of change in your environment at a time, which i understand and practice with my feeding... but this immediate switch to 12/12 will kick her in the a$$ and get her goin rather than her guessing if she should be vegging or getting ready to flower