Possibly range? At that scale the max representable duration is about 16.5 years (assuming they're 64 bits, IIUC the standard mandates that as a minimum) which

Possibly range? At that scale the max representable duration is about 16.5 years (assuming they're 64 bits, IIUC the standard mandates that as a minimum) which could be limiting - although that seems unlikely to be a concern in the framerate domain, but who knows what it might get used for when that might become an issue.