If it's just for benchmarks, why not make it a preference (defaulted off), so benchmarks can be run with the default settings (off) just fine, but people can turn it on if they want to?
Displaying seconds is a valuable feature, so it's not a matter of having unnecessary code. As for being slow, the ability to display seconds was removed because of the minimum system requirements for Windows. Anyone with a machine that has more than the bare minimum can probably spare the kilobytes necessary to draw seconds.