The length should be the finished product as it goes on the bow. Whether it's twisted or not is a matter of who makes the string. If you get a gander at any of the GOOD after market strings you'll notice that they often have one revolution (twist) for each 1 1/2" to 2" of length.

For example, if you shoot a single cam bow with a 100" string then it should normally have 50 twists or more. Most generic factory strings may have about 10 or so. That's one of the reasons (among others) that they creep so badly.