Your question would be a lot easier to answer if you had an accurate drawing or even a picture of the turns and the roadway before and after the turns. The answer to your question really depends on what type of turns are just before and just after the "S" turns. For example, let's say that there is a long straight just before the first "S" turn and a bunch of slow-speed, tight turns just after the last "S" turn. You would want to maximize your speed from the straight by braking very late at the end of the straight, which will probably necessitate a later apex on the first "S" turn. In this example, you're carrying as much speed as possible for as long as possible and giving up what might be the "proper" line for the first "S" turn.

Another example: let's say that preceding the first "S" turn are a bunch of slow-speed, tight turns, and there is a long straight after the last "S" turn. In this example, you want to carry as much speed out of the last "S" turn so that you can maximize the amount of momentum you have down the straight. To properly exit the last "S" turn before the straight, you may have to go slower than could otherwise be possible on the entry to the first "S".

So, in short, my point is: the correct line for each turn should be considered in the context of the immediately preceding and following turns.

And, don't forget that lines frequently change while you are in a real race ("defensive line" vs. "proper line").

I hope this helps.

P.