Correct - you want to delay the closest speaker.

So sitting in the left hand side of the car you would want to delay the left hand speaker. The distance is just an approximation of the delay times the speed of sound. i.e. 3.33cm is about how far sound will travel in 0.1ms (I took the speed of sound as 1200km/h).

So e.g. if your right speaker is 1.3m away and your left speaker is 0.3m away you would want to move the left out by about 1m. So you would set the delay to 3.0ms to move the left speaker 1m further away.