public List<PointOfTime> assembleDurationPoints() {
        return DurationUtils.INSTANCE.getDurationPoints(step, getStartTimeBucket(), getEndTimeBucket());
    }
Assemble time point based on {@link #step} and {@link #start} / {@link #end}
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/input/Duration.java