It's impossible to tell when you should flip your plants to flower without knowing the dimensions of your grow room, the power of your light, the number of plants, and any potential timeline restrictions. Contradictory to what people here have said, vegging for a long time doesn't always increase the yield. The shortest way to get a high yield in a small amount of time is to go Sea of Green style, and get a lot of small identical plants. I think that if your grow area is more than 6ft x 6ft x 6ft, you will get more yield in a shorter time if you grow Sea of Green style, which involves only 1-2 weeks of veg. If your floor area is less than 36 square feet, I'd advise about 3-5 weeks of veg, depending on the height, and then flip it to flowering. Ice will stretch about 100% or so, depending on the particular plant