When working with short sound waves there are sometimes waves that are 0.23 milliseconds of a second and even lower 0.041 milliseconds of a second. In seconds they are 0.00023 sec. and 4.1e-5 sec. They are also 230 microseconds and 41 microseconds of a millisecond.
How do we pronounce these fractions?
A second has 1000 milliseconds. A millisecond has 1000 microseconds.
None of the figures you listed here require "of a second/millisecond". Because a millisecond and a microsecond are their units of measure, they can stand alone.
You would use "of a second" when refer to expressions of partiality. For instance, you might say a third of a second. A thousandth of a second (which is a millisecond, anyways).
You can just use milliseconds/microseconds.
