public long getSinceTime() {
        return this.sinceTime.get();
    }
SinceTime, store the start time of the metric items set

After calling the snapshot() function, it need to be updated to the snapshot time.
inlong-tubemq/tubemq-core/src/main/java/org/apache/inlong/tubemq/corebase/metric/impl/SinceTime.java