Well, about that. The number you find is the maximum number of t-states you have to wait until the screen is ready. In reality, the actual number you have to wait varies by quite a bit. For instance, I made a program that tracked how many t-states the screen needed at that moment in time. What I found is that the amount needed was random and was spread out over about 20 t-states. This means that the 70 t-state screen will actually be ready to go in 50 t-states occasionally.

However, the short answer you want is yes, once you find the delay, it will never change.