private Duration getDayDurationFromTimestamp(long timeTS) {
        Duration duration = new Duration();
        DateTime dt = new DateTime(timeTS);
        duration.setStep(Step.DAY);
        duration.setStart(dt.toString(DurationUtils.YYYY_MM_DD));
        duration.setEnd(dt.toString(DurationUtils.YYYY_MM_DD));
        return duration;
    }
OAP adopt time step by start/end,
reserve step/timeout param to keep consistent with API protocol.
oap-server/server-query-plugin/promql-plugin/src/main/java/org/apache/skywalking/oap/query/promql/handler/PromQLApiHandler.java