You can't actually flower "too early". You can run plants 12/12 from seedling and they will veg for 5-6 weeks usually and then start to flower. They won't get nearly as large as giving them a proper veg, but they will grow and flower.
Counting from flower formation eliminates this genetic/maturity variable. If you start counting plants at 12/12 then the actual time that they are flowering for can be anywhere from 7-21 days wrong. So your time you count will not be an accurate idea of how long the plants took to fully mature. Breeders time frames can be wildly inaccurate based on the phenotypes of the plant. I actually discourage counting days at all since it's mostly arbitrary. Keeping rough track of the weeks won't hurt, but it won't make them finish at a certain time, it will only be a future reference for yourself if you continue to run clones of that plant.