You're right, you do need to adjust for cable length if your cables are long enough.

Since electricity passes through a cable at essentially (close enough for our purposes) light speed - 186,000 miles/second - and since a millisecond - the proposed adjustment resolution - is 1/1000th of a second, you would need to adjust to compensate for each 186 miles or 982,080 ft of cable. This of course is important when you buy your cable in 1,000,000 ft lengths.