System doesn't give you 1 nanosecond precision really. It varies by OS+hardware, from what I remember you may get like 641 nanosecond precision. The number is nanoseconds, yes, but you never get "next nanosecond". In other words, every number you get has the same mod 641. In other systems you may get like 40,000 precision or even worse on SPECTRE/MELTDOWN-protected systems.