protected long getDurationInMinute() {
        if (isMinuteBucket()) {
            return 1;
        } else if (isHourBucket()) {
            return 60;
        } else if (isDayBucket()) {
            return 24 * 60;
        }
        throw new IllegalStateException("Time bucket (" + timeBucket + ") can't be recognized.");
    }
Always get the duration for this time bucket in minute.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/metrics/Metrics.java