You can use the # format specifier after the seconds to specify milliseconds.
For example, you might be using the format string "hh:nn:ss" to currently specify hour, minute, and second. You could add a "." and a "#" for every digit to the right of the decimal to specify milliseconds. For example, if you wanted to specify hour, minute, second, and 2 decimals for the milliseconds, the format string would be "hh:nn:ss.##".
- Elton