That's incorrect. White Widows, like all other strains, will at least double in size, but it won't triple, like Super Silver Haze.
You want to think about flipping them soon. I'd say at 14" to 16".
Height isn't what you want to be achieving, as much as topping to get several tops and spread your branches out. Grow wide, not tall. Use a net to help control height and force the branches apart to allow more light to the lower parts.
The thing about growing tall is, it doesn't matter how tall they get, because your usable light is only going to penetrate the canopy about 12" deep. That's if you have a three ft plant, or a six ft plant. So by growing them taller and taller, you're just wasting time vegging. You may be unnecessarily spending an extra week or two in veg, when that time could be in flower, getting you a harvest earlier.