To show fractional seconds in the HUD message, you would need to change the AUTO_RESTART value in the lang files (for all lanugages) to use "%.3f" instead of "%i" or "%d" and then change floatround(fSec) to fSec.
But note it will probably look really strange because it only updates the value once every second.
And whats the possbile way to make it update every millisecond?