do_add_field(a_time, hours, extra, 24, add_days);
do_add_time_field(a_time, hours, extra, 24, add_days);
add_hours(ha_time_t *a_time, int extra) {	if(extra < 0) {		sub_hours(a_time, -extra);	} else {		do_add_field(a_time, hours, extra, 24, add_days);	}}