Target a good print at Grade 2 filtration in your enlarger.
The proof is in the prints that you make and how they look to your eyes. There is simply no other way of evaluating your negatives, for your process, other than printing them.
- If you get too much contrast for a good straight Grade 2 print, you developed your film for too long.
- If you get too little contrast, you didn't develop the film long enough.
Also remember that another photographer (or Kodak) may give you a recommendation of how long to develop your film, but you may not like the same end results as they do. This is why finding a developing time that works for you is so important. We are all different, work differently, and like different results, so what works for me may not at all work for you.
It is safe to say that Kodak's recommended developing times are a good starting point. But it is only that, a starting point. The rest is up to you.