tv2hrt
first = tv2hrt(&aitv.it_value);
interval = tv2hrt(&aitv.it_interval);
when.cyt_when = (ts = gethrtime() + tv2hrt(&aitv.it_value));
when.cyt_interval = tv2hrt(&aitv.it_interval);
extern hrtime_t tv2hrt(struct timeval *);