public Builder ttl(long ttl, TimeUnit ttlUnit) {
      if (ttlUnit == null) throw new NullPointerException("ttlUnit == null");
      this.ttl = ttl;
      this.ttlUnit = ttlUnit;
      return this;
    }
When {@link #shouldInvoke(Object)} returns true, it will return false until this duration
expires.
zipkin/src/main/java/zipkin2/internal/DelayLimiter.java