public static final StartTime relative(Duration relativeStart) {
        return new StartTime(StartTimeOption.RELATIVE, relativeStart, null);
    }
@Test
    public void testStopRelative() {
        StopTime st = StopTime.relative(Duration.ofMinutes(20));
        assertEquals(StopTimeOption.RELATIVE, st.option());
        assertEquals(20 * 60, st.relativeTime().getSeconds());
        assertNull(st.absoluteTime());
    }