After doing some tests, is seems like changing the defaults does not increase the accuracy for most cases, but what range of distances are you trying to measure?
You might try 500ms and to double the number of measurements you are averaging, but again, your setup might vary. Also, it seems like the material does have a small effect on measurement range and that the average of a bunch of measurements does not always equal the true distance. It seems like it might not be very practical to get a range that is more accurate than a few millimeters. This other ongoing thread might be useful for you:
-Nathan