Generally not necessary to add cal/mag until one nears flowering if in Fox Farm soils. One exception is if you are using high intensity lighting, which increases cal/mag demand.
It is indeed hard to hurt a plant with excess cal/mag, certainly far less probability than adding nitrogen, where we regularly see toxicity problems.
Imho people rely far too much on throwing cal/mag at problems assuming it will fix whatever issue is seen. I don’t see many issues that are truly cal/mag deficiencies. People get away with throwing cal/mag at plants precisely because it’s hard to hurt a plant with cal/mag. Others’ may disagree, but that is my opinion and I’ll stand by that opinion.
I grow in HF and have never needed to add cal/mag until flowering (8 - 12 weeks of veg.) I start adding it at 5ml per gallon (one gallon only) at the beginning of flowering with each watering. I’ve never had problems with it.