struct timeval represents and instant in time with two members, tv_sec (seconds) and tv_usec (microseconds). In this representation, tv_usec is not by itself an absolute time it is a sub second offset off of tv_sec.
struct timespec works the same way except that instead of microseconds it's offset (tv_nsec) is stored in nanosecond units.
The question is: Is there a standard way to convert between these two?
Looking at this doc, I would think multiplying tv_usec by 1000 is sufficient to get tv_nsec.
More important, I suspect is the source of the different structures: they could be filled by different clocks.