particle physics - What is the highest accuracy of measuring time differences achievable today?

I was wondering if it would be possible to shorten the distance between detectors when measuring the speed of neutrinos to, say, 7m rather than the current ~700km? In this way the distance traveled would be known directly. Something similar to the coincidence measurements we now do when studying positronium. Is there a limit to the technology used for timing of events or it is only a matter of technical development and there's room for achieving a greater accuracy than the currently known?