code: public List<Integer> getValidWindows() {
          if (!this.enabled.get()) {
              return EMPTY_WIN;
          }
  
          long diff = TimeUtils.current_time_secs() - this.lastFlushTime + FLUSH_INTERVAL_BIAS;
          if (diff < minWindow) {
              // logger.warn("no valid windows for metric:{}, diff:{}", this.metricName, diff);
              return EMPTY_WIN;
          }
          // for gauge & netty metrics, use only 1min window
          if (this instanceof AsmGauge || this.metricName.startsWith(MetaType.NETTY.getV())) {
              return nettyWindows;
          }
  
          return windowSeconds;
      }
docs: DO NOT judge whether to flush by 60sec because there might be nuance by the alignment of time(maybe less than 1 sec?)
  so we subtract 5 sec from a min flush window.