numeral-js supports formatting a number of seconds in HH:MM:SS format (by typing 00:00:00). Unfortunately it seems that 00:00:00.[000] does not produce a format with milliseconds. When times are short (or can vary from few seconds to minutes), this could be nice to have.

I think it'd be rather simple to implement in the same style as the existing code - it just checks for the existence of : to determine whether to format as time - so there could just be a switch for . (possibly count zeros after for precision) to determine whether to format fractional seconds.