So it sounds to me like you really need to understand your grow setup and what your set up can provide to really know when you need to start providing nutrients. Which means experience and not going off what the nute bottles suggest.
If you use the same soil, light, etc over and over and are finding that on week X, the plant is lacking something, you know the next time to add nutrients around that time to compensate.
Maybe you can be reactive the first few times that happens but then can be proactive in later grows.
Does that sound about right?